



Network Working Group                                       L. Dusseault
Internet-Draft                                  Data Transfer Initiative
Intended status: Informational                                 A. Wright
Expires: 30 August 2026                                                 
                                                              H. Andrews
                                                        26 February 2026


                              JSON Schema
                     draft-dusseault-json-schema-00

Abstract

   JSON Schema defines the media type "application/schema+json", a JSON-
   based format for describing the structure of JSON data.  JSON Schema
   asserts what a JSON document must look like, ways to extract
   information from it, and how to interact with it.  The "application/
   schema-instance+json" media type provides additional feature-rich
   integration with "application/schema+json" beyond what can be offered
   for "application/json" documents.

Discussion Venues

   This note is to be removed before publishing as an RFC.

   Discussion of this document takes place on the JavaScript Object
   Notation Working Group mailing list (json@ietf.org), which is
   archived at https://mailarchive.ietf.org/arch/browse/json.

   Source for this draft and an issue tracker can be found at
   https://github.com/lisad/ietf-json-schema.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 30 August 2026.



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Copyright Notice

   Copyright (c) 2026 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   6
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   6
   2.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     2.1.  Vocabularies  . . . . . . . . . . . . . . . . . . . . . .   7
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   8
   4.  Overall Definitions and Requirements  . . . . . . . . . . . .   9
     4.1.  JSON Schema Documents . . . . . . . . . . . . . . . . . .  10
       4.1.1.  Trivial schema documents  . . . . . . . . . . . . . .  10
       4.1.2.  Root Schema and Subschemas and Resources  . . . . . .  10
     4.2.  Instance  . . . . . . . . . . . . . . . . . . . . . . . .  11
       4.2.1.  Input Equality  . . . . . . . . . . . . . . . . . . .  12
     4.3.  Keywords  . . . . . . . . . . . . . . . . . . . . . . . .  13
     4.4.  Fragment Identifiers  . . . . . . . . . . . . . . . . . .  14
     4.5.  Other General Considerations  . . . . . . . . . . . . . .  14
       4.5.1.  Range of JSON Values  . . . . . . . . . . . . . . . .  14
       4.5.2.  Requirements for handling extensions  . . . . . . . .  14
       4.5.3.  Validation  . . . . . . . . . . . . . . . . . . . . .  15
   5.  Core Keywords . . . . . . . . . . . . . . . . . . . . . . . .  15
     5.1.  Environment . . . . . . . . . . . . . . . . . . . . . . .  16
       5.1.1.  "$schema" . . . . . . . . . . . . . . . . . . . . . .  16
       5.1.2.  "$vocabulary" . . . . . . . . . . . . . . . . . . . .  16
       5.1.3.  "$id" . . . . . . . . . . . . . . . . . . . . . . . .  18
       5.1.4.  "$anchor" and "$dynamicAnchor"  . . . . . . . . . . .  19
     5.2.  Definitions and References  . . . . . . . . . . . . . . .  20
       5.2.1.  "$ref" and "$dynamicRef"  . . . . . . . . . . . . . .  20
       5.2.2.  "$defs" . . . . . . . . . . . . . . . . . . . . . . .  21
     5.3.  "$comment"  . . . . . . . . . . . . . . . . . . . . . . .  22
   6.  Subschema keywords  . . . . . . . . . . . . . . . . . . . . .  23
     6.1.  Keyword Independence  . . . . . . . . . . . . . . . . . .  23
     6.2.  Keywords for Applying Subschemas in Place . . . . . . . .  23
       6.2.1.  "allOf" . . . . . . . . . . . . . . . . . . . . . . .  24
       6.2.2.  "anyOf" . . . . . . . . . . . . . . . . . . . . . . .  24



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       6.2.3.  "oneOf" . . . . . . . . . . . . . . . . . . . . . . .  24
       6.2.4.  "not" . . . . . . . . . . . . . . . . . . . . . . . .  24
       6.2.5.  "if"  . . . . . . . . . . . . . . . . . . . . . . . .  25
       6.2.6.  "then"  . . . . . . . . . . . . . . . . . . . . . . .  25
       6.2.7.  "else"  . . . . . . . . . . . . . . . . . . . . . . .  25
       6.2.8.  "dependentSchemas"  . . . . . . . . . . . . . . . . .  26
     6.3.  Keywords for Applying Subschemas to Arrays  . . . . . . .  26
       6.3.1.  "prefixItems" . . . . . . . . . . . . . . . . . . . .  26
       6.3.2.  "items" . . . . . . . . . . . . . . . . . . . . . . .  26
       6.3.3.  "contains"  . . . . . . . . . . . . . . . . . . . . .  27
     6.4.  Keywords for Applying Subschemas to Objects . . . . . . .  28
       6.4.1.  "properties"  . . . . . . . . . . . . . . . . . . . .  28
       6.4.2.  "patternProperties" . . . . . . . . . . . . . . . . .  28
       6.4.3.  "additionalProperties"  . . . . . . . . . . . . . . .  29
       6.4.4.  "propertyNames" . . . . . . . . . . . . . . . . . . .  29
   7.  Keywords for Unevaluated Locations  . . . . . . . . . . . . .  30
     7.1.  Keyword Independence  . . . . . . . . . . . . . . . . . .  31
     7.2.  "unevaluatedItems"  . . . . . . . . . . . . . . . . . . .  31
     7.3.  "unevaluatedProperties" . . . . . . . . . . . . . . . . .  32
   8.  Keywords for Structural Validation  . . . . . . . . . . . . .  32
     8.1.  Validation Keywords for Any Instance Type . . . . . . . .  33
       8.1.1.  "type"  . . . . . . . . . . . . . . . . . . . . . . .  33
       8.1.2.  "enum"  . . . . . . . . . . . . . . . . . . . . . . .  33
       8.1.3.  "const" . . . . . . . . . . . . . . . . . . . . . . .  33
     8.2.  Validation Keywords for Numeric Inputs (number and
           integer)  . . . . . . . . . . . . . . . . . . . . . . . .  34
       8.2.1.  "multipleOf"  . . . . . . . . . . . . . . . . . . . .  34
       8.2.2.  "maximum" . . . . . . . . . . . . . . . . . . . . . .  34
       8.2.3.  "exclusiveMaximum"  . . . . . . . . . . . . . . . . .  34
       8.2.4.  "minimum" . . . . . . . . . . . . . . . . . . . . . .  34
       8.2.5.  "exclusiveMinimum"  . . . . . . . . . . . . . . . . .  34
     8.3.  Validation Keywords for Strings . . . . . . . . . . . . .  34
       8.3.1.  "maxLength" . . . . . . . . . . . . . . . . . . . . .  34
       8.3.2.  "minLength" . . . . . . . . . . . . . . . . . . . . .  35
       8.3.3.  "pattern" . . . . . . . . . . . . . . . . . . . . . .  35
     8.4.  Validation Keywords for Arrays  . . . . . . . . . . . . .  35
       8.4.1.  "maxItems"  . . . . . . . . . . . . . . . . . . . . .  35
       8.4.2.  "minItems"  . . . . . . . . . . . . . . . . . . . . .  35
       8.4.3.  "uniqueItems" . . . . . . . . . . . . . . . . . . . .  36
       8.4.4.  "maxContains" . . . . . . . . . . . . . . . . . . . .  36
       8.4.5.  "minContains" . . . . . . . . . . . . . . . . . . . .  36
     8.5.  Validation Keywords for Objects . . . . . . . . . . . . .  36
       8.5.1.  "maxProperties" . . . . . . . . . . . . . . . . . . .  36
       8.5.2.  "minProperties" . . . . . . . . . . . . . . . . . . .  37
       8.5.3.  "required"  . . . . . . . . . . . . . . . . . . . . .  37
       8.5.4.  "dependentRequired" . . . . . . . . . . . . . . . . .  37
   9.  Vocabularies for Semantic Content With "format" . . . . . . .  37
     9.1.  Foreword  . . . . . . . . . . . . . . . . . . . . . . . .  37



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     9.2.  Implementation Requirements . . . . . . . . . . . . . . .  39
       9.2.1.  Format-Annotation Vocabulary  . . . . . . . . . . . .  39
       9.2.2.  Format-Assertion Vocabulary . . . . . . . . . . . . .  39
       9.2.3.  Custom format attributes  . . . . . . . . . . . . . .  41
     9.3.  Defined Formats . . . . . . . . . . . . . . . . . . . . .  41
       9.3.1.  Dates, Times, and Duration  . . . . . . . . . . . . .  41
       9.3.2.  Email Addresses . . . . . . . . . . . . . . . . . . .  42
       9.3.3.  Hostnames . . . . . . . . . . . . . . . . . . . . . .  42
       9.3.4.  IP Addresses  . . . . . . . . . . . . . . . . . . . .  43
       9.3.5.  Resource Identifiers  . . . . . . . . . . . . . . . .  43
       9.3.6.  Templates . . . . . . . . . . . . . . . . . . . . . .  44
       9.3.7.  JSON Pointers . . . . . . . . . . . . . . . . . . . .  44
       9.3.8.  Expressions . . . . . . . . . . . . . . . . . . . . .  45
   10. A Vocabulary for the Contents of String-Encoded Data  . . . .  45
     10.1.  Foreword . . . . . . . . . . . . . . . . . . . . . . . .  45
     10.2.  Implementation Requirements  . . . . . . . . . . . . . .  46
     10.3.  "contentEncoding"  . . . . . . . . . . . . . . . . . . .  46
     10.4.  "contentMediaType" . . . . . . . . . . . . . . . . . . .  47
     10.5.  "contentSchema"  . . . . . . . . . . . . . . . . . . . .  47
     10.6.  Example  . . . . . . . . . . . . . . . . . . . . . . . .  47
   11. A Vocabulary for Basic Meta-Data Annotations  . . . . . . . .  49
     11.1.  "title" and "description"  . . . . . . . . . . . . . . .  49
     11.2.  "default"  . . . . . . . . . . . . . . . . . . . . . . .  49
     11.3.  "deprecated" . . . . . . . . . . . . . . . . . . . . . .  49
     11.4.  "readOnly" and "writeOnly" . . . . . . . . . . . . . . .  50
     11.5.  "examples" . . . . . . . . . . . . . . . . . . . . . . .  51
   12. Loading and Processing Schemas  . . . . . . . . . . . . . . .  51
     12.1.  Loading a Schema . . . . . . . . . . . . . . . . . . . .  51
       12.1.1.  Initial Base URI . . . . . . . . . . . . . . . . . .  51
       12.1.2.  Loading a referenced schema  . . . . . . . . . . . .  52
       12.1.3.  Detecting a Meta-Schema  . . . . . . . . . . . . . .  53
     12.2.  Dereferencing  . . . . . . . . . . . . . . . . . . . . .  53
       12.2.1.  Relative References  . . . . . . . . . . . . . . . .  54
       12.2.2.  JSON Pointer fragments and embedded schema
               resources . . . . . . . . . . . . . . . . . . . . . .  55
     12.3.  Compound Documents . . . . . . . . . . . . . . . . . . .  57
       12.3.1.  Bundling . . . . . . . . . . . . . . . . . . . . . .  57
       12.3.2.  Differing and Default Dialects . . . . . . . . . . .  58
       12.3.3.  Validating . . . . . . . . . . . . . . . . . . . . .  58
     12.4.  Caveats  . . . . . . . . . . . . . . . . . . . . . . . .  58
       12.4.1.  Guarding Against Infinite Recursion  . . . . . . . .  59
       12.4.2.  References to Possible Non-Schemas"  . . . . . . . .  59
     12.5.  RESTful / Hypermedia Schema References . . . . . . . . .  59
       12.5.1.  Linking to a Schema  . . . . . . . . . . . . . . . .  60
       12.5.2.  Usage Over HTTP  . . . . . . . . . . . . . . . . . .  60
   13. Keyword Behaviors . . . . . . . . . . . . . . . . . . . . . .  60
     13.1.  Lexical Scope and Dynamic Scope  . . . . . . . . . . . .  61
     13.2.  Keyword Interactions . . . . . . . . . . . . . . . . . .  62



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     13.3.  Default Behaviors  . . . . . . . . . . . . . . . . . . .  62
     13.4.  Handling unrecognized or unsupported keywords  . . . . .  63
     13.5.  Identifiers  . . . . . . . . . . . . . . . . . . . . . .  63
     13.6.  Applicators  . . . . . . . . . . . . . . . . . . . . . .  64
       13.6.1.  Referenced and Referencing Schemas . . . . . . . . .  64
     13.7.  Assertions . . . . . . . . . . . . . . . . . . . . . . .  65
       13.7.1.  Assertions and Input Primitive Types . . . . . . . .  65
     13.8.  Annotations  . . . . . . . . . . . . . . . . . . . . . .  66
       13.8.1.  Collecting Annotations . . . . . . . . . . . . . . .  66
     13.9.  Reserved Locations . . . . . . . . . . . . . . . . . . .  70
     13.10. Loading Input Data . . . . . . . . . . . . . . . . . . .  70
   14. Output Formatting . . . . . . . . . . . . . . . . . . . . . .  70
     14.1.  Format . . . . . . . . . . . . . . . . . . . . . . . . .  70
     14.2.  Output Formats . . . . . . . . . . . . . . . . . . . . .  70
     14.3.  Minimum Information  . . . . . . . . . . . . . . . . . .  71
       14.3.1.  Keyword Relative Location  . . . . . . . . . . . . .  71
       14.3.2.  Keyword Absolute Location  . . . . . . . . . . . . .  72
       14.3.3.  Instance Location  . . . . . . . . . . . . . . . . .  72
       14.3.4.  Error or Annotation  . . . . . . . . . . . . . . . .  72
       14.3.5.  Nested Results . . . . . . . . . . . . . . . . . . .  72
     14.4.  Output Structure . . . . . . . . . . . . . . . . . . . .  73
       14.4.1.  Flag . . . . . . . . . . . . . . . . . . . . . . . .  74
       14.4.2.  Basic  . . . . . . . . . . . . . . . . . . . . . . .  74
       14.4.3.  Detailed . . . . . . . . . . . . . . . . . . . . . .  75
       14.4.4.  Verbose  . . . . . . . . . . . . . . . . . . . . . .  77
       14.4.5.  Output validation schemas  . . . . . . . . . . . . .  78
   15. Extensibility . . . . . . . . . . . . . . . . . . . . . . . .  78
     15.1.  Non-JSON Inputs  . . . . . . . . . . . . . . . . . . . .  78
     15.2.  Schema Vocabularies  . . . . . . . . . . . . . . . . . .  79
     15.3.  Meta-Schemas . . . . . . . . . . . . . . . . . . . . . .  79
     15.4.  Default JSON Schema Dialect  . . . . . . . . . . . . . .  80
   16. Security Considerations . . . . . . . . . . . . . . . . . . .  81
   17. Interoperability Considerations . . . . . . . . . . . . . . .  82
     17.1.  Programming Language Independence  . . . . . . . . . . .  82
     17.2.  Mathematical Integers  . . . . . . . . . . . . . . . . .  82
     17.3.  Regular Expressions  . . . . . . . . . . . . . . . . . .  82
   18. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  83
     18.1.  application/schema+json  . . . . . . . . . . . . . . . .  83
     18.2.  application/schema-instance+json . . . . . . . . . . . .  83
   19. References  . . . . . . . . . . . . . . . . . . . . . . . . .  84
     19.1.  Normative References . . . . . . . . . . . . . . . . . .  84
     19.2.  Informative References . . . . . . . . . . . . . . . . .  86
   Appendix A.  Schema identification examples . . . . . . . . . . .  87
   Appendix B.  Manipulating schema documents and references . . . .  90
     B.1.  Bundling schema resources into a single document  . . . .  90
     B.2.  Reference removal is not always safe  . . . . . . . . . .  90
   Appendix C.  Example of recursive schema extension  . . . . . . .  91
   Appendix D.  Working with vocabularies  . . . . . . . . . . . . .  93



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     D.1.  Best practices for vocabulary and meta-schema authors"  .  93
     D.2.  Example meta-schema with vocabulary declarations  . . . .  94
   Appendix E.  References and generative use cases  . . . . . . . .  96
   Appendix F.  Acknowledgments  . . . . . . . . . . . . . . . . . .  97
   Appendix G.  Change Log . . . . . . . . . . . . . . . . . . . . .  98
     G.1.  draft-dusseault-json-schema-00  . . . . . . . . . . . . .  98
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  98

1.  Introduction

   ...

   JSON Schemas are JSON documents that describe and constrain other
   JSON documents.  JSON Schema defines validation, documentation,
   hyperlink navigation, and interaction control of JSON data.

   This specification defines JSON Schema core terminology and
   mechanisms, including pointing to another JSON Schema by reference,
   dereferencing a JSON Schema reference, specifying the dialect being
   used, specifying a dialect's vocabulary requirements, and defining
   the expected output.

   The status of this document is literally a draft, and it is not ready
   for implementors to adopt in place of widely implemented versions of
   JSON Schema.  It is a proposed starting point for a WG and a wide
   consensus process.

1.1.  Notational Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   The terms "JSON", "JSON text", "JSON value", "member", "element",
   "object", "array", "number", "string", "boolean", "true", "false",
   and "null" in this document are to be interpreted as defined in
   [RFC8259].

2.  Overview

   JSON Schemas are JSON documents that describe and constrain other
   JSON documents through keywords and keyword behaviors.  The
   specification registers the "application/schema+json" media type to
   identify a JSON Schema resource, and the "application/schema-
   instance+json" media type to identify a resource that can be
   validated against a JSON Schema.





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   The result of validating a JSON document against a JSON Schema can be
   framed as rules that decide if an _input_ is in the _valid set_
   according to that schema, . An input in the valid set is considered
   an _instance_ of the schema.

   JSON Schema uses _keywords_ to assert constraints on JSON documents
   or provide annotations with additional information.  Additional
   keywords combine other keywords or provide references to sub-schemas,
   features which allow more complex JSON data structures.

   In formal language theory, JSON Schema resembles a context-free
   language, as most keywords are context-free.  Thus, JSON instances
   can be validated quickly and simply, without I/O or querying data
   elsewhere in the same JSON instance.

   This document defines a core vocabulary of keywords that MUST be
   supported by any implementation.  Its keywords are each prefixed with
   a "$" character to emphasize their required nature.  This vocabulary
   is essential to the functioning of the "application/schema+json"
   media type, and is used to bootstrap the loading of other
   vocabularies.

   Additionally, this document defines a RECOMMENDED vocabulary of
   keywords for applying subschemas conditionally, and for applying
   subschemas to the contents of objects and arrays.  Either this
   vocabulary or one very much like it is required to write schemas for
   non-trivial JSON instances, whether those schemas are intended for
   assertion validation, annotation, or both.  While not part of the
   required core vocabulary, for maximum interoperability this
   additional vocabulary is included in this document and its use is
   strongly encouraged.

2.1.  Vocabularies

   To facilitate re-use, keywords can be organized into vocabularies.  A
   vocabulary consists of a list of keywords, together with their syntax
   and semantics.  A dialect is defined as a set of vocabularies and
   their required support identified in a meta-schema.  Vocabularies,
   dialects and meta-schemas are not required features for most schema
   authors to understand, but must be understood by authors of meta-
   schemas and handled by implementors of validation or other JSON
   Schema processing software.









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   JSON Schema can be extended either by defining additional
   vocabularies, or less formally by defining additional keywords
   outside of any vocabulary.  Unrecognized individual keywords simply
   have their values treated as annotations, while the behavior with
   respect to an unrecognized vocabulary can be controlled when
   declaring which vocabularies are in use.

3.  Terminology

   These terms are all defined in the context of JSON Schema.  These
   quick definitions may not be enough to completely comprehend roles
   and uses, but may still provide a useful quick reference.

   *JSON Document*

   A JSON document is an information resource (series of octets)
   described by the application/json media type.

   *Input*

   A JSON document supplied to a validator or other implementation, in
   order to compare it to a schema, is an input until it is known to be
   in the valid set for that schema.

   *Instance*

   A JSON document that is in the valid set for a given schema is an
   _instance_ of that schema.

   *Object*

   _Object_ is defined for JSON in [RFC8259] and has the same meaning
   here.

   *Schema / Schema Document*

   A JSON Schema document, or simply a _schema_, is a JSON document used
   to describe and constrain JSON Documents.  Used in validation, the
   schema defines the valid set, or all possible instances that validate
   successfully.  As a JSON document, a schema may also be an instance
   of some meta-schema.

   *Schema Resource*

   A JSON _Schema resource_ is a schema uniquely identified by a URI, in
   contrast to an anonymous schema which has no URI.  A schema is
   canonically identified (in the sense of [RFC6596]) by an absolute URI
   ([RFC3986], Section 4.3).



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   *Keyword*

   JSON Schema works by defining keywords with specific behavior.  A
   _keyword_ appears as a JSON _name_ [RFC8259].  Not all JSON names in
   a schema are keywords, but all keywords have required behavior.

   *Vocabulary*

   A _vocabulary_ is a set of keywords that are defined to enable some
   functionality, particularly when JSON Schema is extended with
   external vocabularies.

   *Meta-Schema*

   A _meta-schema_ describes and constrains schemas which may be
   instances of the meta-schema.

   *Root schema*

   The root schema is the top-level schema object that serves as the
   starting point and container for all of a schema's rules and
   annotations.  It typically defines the Base URI for the entire
   document.

   *Subschema*

   A subschema is a schema that happens to be located inside another
   schema.  Structural keywords like 'items' and 'properties' use
   subschemas to describe structure inside arrays and objects.
   Aggregation keywords like 'anyOf' and 'not' direct how to apply the
   subschemas they hold.

   A subschema can be directly inside its parent schema, can be
   elsewhere in the Schema Document (using a fragment reference), or in
   a separate document (using an absolute reference).

   *Implementation*

   An implementation is software that implements this specification.
   Some implementations validate inputs, but some implementations
   generate documentation, data or code based on a schema.

4.  Overall Definitions and Requirements

   This section is the start of normative requirements especially for
   implementations.  However, a practitioner may wish to check the basic
   meaning of terms defined above and skip toSection 13 where specific
   keywords and purposes begin to be defined.



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4.1.  JSON Schema Documents

   A JSON Schema, with its specific rules or constraints to describe and
   validate JSON data, is represented in digital form as a JSON schema
   document.

   A JSON Schema MUST be an _object_ or a boolean.  When a schema is an
   object, it can be seen to be a schema from the '$schema' keyword in
   the object.  See below for special treatment of the boolean schemas.

   Schemas are used to validate inputs that may be instances
   (Section 4.2) of the schema, but each schema can itself be
   interpreted as an instance (see Section 15.3 for when and how this
   happens).

   Schema documents SHOULD always be given the media type "application/
   schema+json", even when playing the role of an instance.

4.1.1.  Trivial schema documents

   The schema values "true" and "false" are trivial schemas.  The valid
   set for the 'true' schema is all possible JSON documents, and the
   valid set for the 'false' schema is empty.  The trivial boolean
   schemas exist to clarify schema author intent and facilitate schema
   processing optimizations.  They behave identically to the following
   schema objects (where "not" is part of the subschema application
   vocabulary defined in this document).

   true  Always passes validation, as if the empty schema {}

   false  Always fails validation, as if the schema { "not": {} }

   While the empty schema object is unambiguous, there are many possible
   equivalents to the "false" schema.  Using the boolean values ensures
   that the intent is clear to both human readers and implementations.

4.1.2.  Root Schema and Subschemas and Resources

   A JSON Schema resource is a schema which is canonically identified
   (in the sense of [RFC6596]) by an absolute URI ([RFC3986],
   Section 4.3).  Schema resources MAY also be identified by URIs,
   including URIs with fragments, if the resulting secondary resource
   (as defined by [RFC3986], Section 3.5) is identical to the primary
   resource.  This can occur with the empty fragment, or when one schema
   resource is embedded in another.  Any such URIs with fragments are
   considered to be non-canonical.





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   The root schema is always a schema resource, where the URI is
   determined as described in Section 12.1.1.
   // Note that documents that embed schemas in another format will not
   // have a root schema resource in this sense.  Exactly how such
   // usages fit with the JSON Schema document and resource concepts
   // will be clarified in a future draft.

   Some keywords take schemas themselves, allowing JSON Schemas to be
   nested:

   {
       "title": "root",
       "items": {
           "title": "array item"
       }
   }

   In this example document, the schema titled "array item" is a
   subschema, and the schema titled "root" is the root schema.

   As with the root schema, a subschema is either an object or a
   boolean.

   As discussed in Section 5.1.3, a JSON Schema document can contain
   multiple JSON Schema resources.  When used without qualification, the
   term "root schema" refers to the document's root schema.  In some
   cases, resource root schemas are discussed.  A resource's root schema
   is its top-level schema object, which would also be a document root
   schema if the resource were to be extracted to a standalone JSON
   Schema document.

   Whether multiple schema resources are embedded or linked with a
   reference, they are processed in the same way, with the same
   available behaviors.

4.2.  Instance

   An instance of a schema is a JSON value or document that is in the
   valid set of a schema.  An instance has one of six primitive types,
   and a range of possible values depending on the type:

   null  A JSON "null" value

   boolean  A JSON "true" or "false" value

   object  An unordered set of properties mapping a string to an
      instance, the JSON "object" value




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   array  An ordered list of instances, with the JSON "array" value

   number  An arbitrary-precision, base-10 decimal number value, from
      the JSON "number" value

   string  A string of Unicode code points, from the JSON "string" value

   Whitespace and formatting concerns, including different lexical
   representations of numbers that are equal within the data model, are
   outside the scope of JSON Schema.  JSON Schema Section 2.1 that wish
   to work with such differences in lexical representations SHOULD
   define keywords to precisely interpret formatted strings within the
   data model rather than relying on having the original JSON
   representation Unicode characters available.

   Since an object cannot have two properties with the same key,
   behavior for a JSON document that tries to define two properties with
   the same key in a single object is undefined.

   Note that JSON Schema vocabularies are free to define their own
   extended type system.  This should not be confused with the core
   types defined here.  As an example, "integer" is a reasonable type
   for a vocabulary to define as a value for a keyword, but the data
   model makes no distinction between integers and other numbers.

4.2.1.  Input Equality

   Two JSON inputs are said to be equal if and only if they are of the
   same type and have the same value according to the JSON data model.
   Specifically, this means:

   *  both are null; or

   *  both are true; or

   *  both are false; or

   *  both are strings, and are the same codepoint-for-codepoint; or

   *  both are numbers, and have the same mathematical value; or

   *  both are arrays, and have an equal value item-for-item; or

   *  both are objects, and each property in one has exactly one
      property with a key equal to the other's, and that other property
      has an equal value.





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   Implied in this definition is that arrays must be the same length,
   objects must have the same number of members, properties in objects
   are unordered, there is no way to define multiple properties with the
   same key, and mere formatting differences (indentation, placement of
   commas, trailing zeros) are insignificant.  Two equal inputs are
   guaranteed to yield identical validation results for a given schema,
   regardless of their original formatting.

4.3.  Keywords

   Object properties that are applied to the instance are called
   keywords, or schema keywords.  Broadly speaking, keywords fall into
   one of five categories:

   identifiers  control schema identification through setting a URI for
      the schema and/or changing how the base URI is determined

   assertions  produce a boolean result when applied to an instance

   annotations  attach information to an instance for application use

   applicators  apply one or more subschemas to a particular location in
      the instance, and combine or modify their results

   reserved locations  do not directly affect results, but reserve a
      place for a specific purpose to ensure interoperability

   Keywords may fall into multiple categories, although applicators
   SHOULD only produce assertion results based on their subschemas'
   results.  They should not define additional constraints independent
   of their subschemas.

   Keywords which are properties within the same schema object are
   referred to as adjacent keywords.

   Extension keywords, meaning those defined outside of this document
   and its companions, are free to define other behaviors as well.

   A JSON Schema MAY contain properties which are not schema keywords or
   are not recognized as schema keywords.  The behavior of such keywords
   is governed by Section 13.4.

   Unknown keywords SHOULD be treated as annotations, where the value of
   the keyword is the value of the annotation.

   An empty schema is a JSON Schema with no properties, or only unknown
   properties.




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4.4.  Fragment Identifiers

   In accordance with section 3.1 of [RFC6839], the syntax and semantics
   of fragment identifiers specified for any +json media type SHOULD be
   as specified for "application/json".  (At publication of this
   document, there is no fragment identification syntax defined for
   "application/json".)

   Additionally, the "application/schema+json" media type supports two
   fragment identifier structures: plain names and JSON Pointers.  The
   "application/schema-instance+json" media type supports one fragment
   identifier structure: JSON Pointers.

   The use of JSON Pointers as URI fragment identifiers is described in
   [RFC6901].  For "application/schema+json", which supports two
   fragment identifier syntaxes, fragment identifiers matching the JSON
   Pointer syntax, including the empty string, MUST be interpreted as
   JSON Pointer fragment identifiers.

   Per the W3C's best practices for fragment identifiers
   ([W3C.WD-fragid-best-practices-20121025]), plain name fragment
   identifiers in "application/schema+json" are reserved for referencing
   locally named schemas.  All fragment identifiers that do not match
   the JSON Pointer syntax MUST be interpreted as plain name fragment
   identifiers.

   Defining and referencing a plain name fragment identifier within an
   "application/schema+json" document are specified in the "$anchor"
   keyword (Section 5.1.4) section.

4.5.  Other General Considerations

4.5.1.  Range of JSON Values

   An instance may be any valid JSON value as defined by JSON
   ([RFC8259]).  JSON Schema imposes no restrictions on type: JSON
   Schema can describe any JSON value, including, for example, null.

4.5.2.  Requirements for handling extensions

   Additional schema keywords and schema vocabularies MAY be defined by
   any entity.  Save for explicit agreement, schema authors SHALL NOT
   expect these additional keywords and vocabularies to be supported by
   implementations that do not explicitly document such support.
   Implementations SHOULD treat keywords they do not support as
   annotations, where the value of the keyword is the value of the
   annotation.




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   Implementations MAY provide the ability to register or load handlers
   for vocabularies that they do not support directly.  The exact
   mechanism for registering and implementing such handlers is
   implementation-dependent.

4.5.3.  Validation

   JSON Schema validation applies the rules of a JSON Schema to
   determine if an input is in the valid set for that schema.  An
   instance location that satisfies all asserted constraints is then
   annotated with any keywords that contain non-assertion information,
   such as descriptive metadata and usage hints.

   Each schema object is independently evaluated against each input
   location to which it applies.  This greatly simplifies implementation
   requirements by ensuring that implementations do not need to maintain
   state across the document-wide validation process.

   This specification defines a set of assertion keywords, as well as a
   small vocabulary of metadata keywords that can be used to annotate
   the JSON instance with useful information.  The Section 9 keyword is
   intended primarily as an annotation, but can optionally be used as an
   assertion.  The Section 10 keywords are annotations for working with
   documents embedded as JSON strings.

5.  Core Keywords

   Core keywords MUST be implemented by any processor indicating support
   for the "application/jsonschema+json" media type.

   The behavior of a false value for this vocabulary (and only this
   vocabulary) is undefined, as is the behavior when "$vocabulary" is
   present but the Core vocabulary is not included.  However, it is
   RECOMMENDED that implementations detect these cases and raise an
   error when they occur.  It is not meaningful to declare that a meta-
   schema optionally uses Core.

   The current URI for the Core vocabulary is:

   <https://json-schema.org/draft/2020-12/vocab/core>.

   The current URI for the corresponding meta-schema is:

   https://json-schema.org/draft/2020-12/meta/core (https://json-
   schema.org/draft/2020-12/meta/core).






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   While the "$" prefix is not formally reserved for the Core
   vocabulary, it is RECOMMENDED that extension keywords (in
   vocabularies or otherwise) begin with a character other than "$" to
   avoid possible future collisions.

5.1.  Environment

   Environment keywords MUST be read by implementations before other
   keywords may be evaluated, as they are capable of impacting the
   behavior of other keywords.

5.1.1.  "$schema"

   The "$schema" keyword is both used as a JSON Schema dialect
   identifier and as the identifier of a resource which is itself a JSON
   Schema, which describes the set of valid schemas written for this
   particular dialect.

   The value of this keyword MUST be a (containing a scheme, per
   [RFC3986], Section 3) and this URI MUST be normalized.  The current
   schema MUST be valid against the meta-schema identified by this URI.

   If this URI identifies a retrievable resource, that resource SHOULD
   be of media type "application/schema+json".

   The "$schema" keyword SHOULD be used in the document root schema
   object, and MAY be used in the root schema objects of embedded schema
   resources.  It MUST NOT appear in non-resource root schema objects.
   If absent from the document root schema, the resulting behavior is
   implementation-defined.

   Values for this property are defined elsewhere in this and other
   documents, and by other parties.

5.1.2.  "$vocabulary"

   The "$vocabulary" keyword is used in meta-schemas to identify the
   vocabularies available for use in schemas described by that meta-
   schema.  It is also used to indicate whether each vocabulary is
   required or optional, in the sense that an implementation MUST
   understand the required vocabularies in order to successfully process
   the schema.  Together, this information forms a dialect.  Any
   vocabulary that is understood by the implementation MUST be processed
   in a manner consistent with the semantic definitions contained within
   the vocabulary.






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   The value of this keyword MUST be an object.  The property names in
   the object MUST be URIs (containing a scheme) and this URI MUST be
   normalized.  Each URI that appears as a property name identifies a
   specific set of keywords and their semantics.

   The URI MAY be a URL, but the nature of the retrievable resource is
   currently undefined, and reserved for future use.  Vocabulary authors
   MAY use the URL of the vocabulary specification, in a human-readable
   media type such as text/html or text/plain, as the vocabulary URI.
   // Vocabulary documents may be added in forthcoming drafts.  For now,
   // identifying the keyword set is deemed sufficient as that, along
   // with meta-schema validation, is how the current "vocabularies"
   // work today.  Any future vocabulary document format will be
   // specified as a JSON document, so using text/html or other non-JSON
   // formats in the meantime will not produce any future ambiguity.

   The values of the object properties MUST be booleans.  If the value
   is true, then implementations that do not recognize the vocabulary
   MUST refuse to process any schemas that declare this meta-schema with
   "$schema".  If the value is false, implementations that do not
   recognize the vocabulary SHOULD proceed with processing such schemas.
   The value has no impact if the implementation understands the
   vocabulary.

   Per Section 4.5.2, unrecognized keywords SHOULD be treated as
   annotations.  This remains the case for keywords defined by
   unrecognized vocabularies.  It is not currently possible to
   distinguish between unrecognized keywords that are defined in
   vocabularies from those that are not part of any vocabulary.

   The "$vocabulary" keyword SHOULD be used in the root schema of any
   schema resource intended for use as a meta-schema.  It MUST NOT
   appear in subschemas.

   The "$vocabulary" keyword MUST be ignored in schema resources that
   are not being processed as a meta-schema.  This allows validating a
   meta-schema M against its own meta-schema M' without requiring the
   implementation to understand the vocabularies declared by M.

5.1.2.1.  Default vocabularies

   If "$vocabulary" is absent, an implementation MAY determine behavior
   based on the meta-schema if it is recognized from the URI value of
   the referring schema's "$schema" keyword.  This is how behavior (such
   as Hyper-Schema usage) has been recognized prior to the existence of
   vocabularies.





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   If the meta-schema, as referenced by the schema, is not recognized,
   or is missing, then the behavior is implementation-defined.  If the
   implementation proceeds with processing the schema, it MUST assume
   the use of the core vocabulary.  If the implementation is built for a
   specific purpose, then it SHOULD assume the use of all of the most
   relevant vocabularies for that purpose.

   For example, an implementation that is a validator SHOULD assume the
   use of all vocabularies in this specification and the companion
   Validation specification.

5.1.2.2.  Non-inheritability of vocabularies

   Note that the processing restrictions on "$vocabulary" mean that
   meta-schemas that reference other meta-schemas using "$ref" or
   similar keywords do not automatically inherit the vocabulary
   declarations of those other meta-schemas.  All such declarations must
   be repeated in the root of each schema document intended for use as a
   meta-schema.  This is demonstrated in the example meta-schema
   (Appendix D.2).
   // This requirement allows implementations to find all vocabulary
   // requirement information in a single place for each meta-schema.
   // As schema extensibility means that there are endless potential
   // ways to combine more fine-grained meta-schemas by reference,
   // requiring implementations to anticipate all possibilities and
   // search for vocabularies in referenced meta-schemas would be overly
   // burdensome.

5.1.2.3.  Updates to Meta-Schema and Vocabulary URIs

   Updated vocabulary and meta-schema URIs MAY be published between
   specification drafts in order to correct errors.  Implementations
   SHOULD consider URIs dated after this specification draft and before
   the next to indicate the same syntax and semantics as those listed
   here.

5.1.3.  "$id"

   The $id keyword identifies a schema resource with its _canonical URI_
   (in the sense of [RFC6596]).  Explicit identification makes it easier
   for a schema to be referenced, especially from other schemas,
   allowing re-use, modularity and extensibility of schemas.  An
   explicit identifier is a more stable way to reference a schema than
   its location (either its URL on the Web or as a location within the
   structure of a parent schema).

   Requirements on $id value:




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   *  MUST be a string

   *  MUST be a valid URI reference ([RFC3986], Section 4.1)

   *  SHOULD be normalized

   *  MUST NOT have a fragment ([RFC3986], Section 3.5)

   The value of an $id may be a full URI or a _relative reference_
   ([RFC3986], Section 4.2).  When a relative URI is used, knowing the
   base URI becomes important.  Read Section 12.2.1 and Appendix A to
   understand how that must be done.

   Note that an URI does not have to be a URL.  Even if it is a URL, the
   URL may not resolve and return a schema, and implementations are
   warned against automatically resolving network references to fetch
   schemas (see Section 12.1.2).  Nevertheless, the URI still identifies
   the schema.

   The presence of "$id" in a subschema indicates that the subschema
   constitutes a distinct schema resource within a single schema
   document.

   See also the $anchor keyword (Section 5.1.4) for naming subschemas,
   and the $ref keyword (Section 5.2.1) in which $id and $anchor values
   are frequently used.

5.1.3.1.  Identifying the root schema

   The root schema of a JSON Schema document SHOULD contain an "$id"
   keyword with an absolute-URI ([RFC3986], Section 4.3; containing a
   scheme, but no fragment).

5.1.4.  "$anchor" and "$dynamicAnchor"

   Using JSON Pointer fragments requires knowledge of the structure of
   the schema.  When writing schema documents with the intention to
   provide re-usable schemas, it may be preferable to use a plain name
   fragment that is not tied to any particular structural location.
   This allows a subschema to be relocated without requiring JSON
   Pointer references to be updated.

   The "$anchor" and "$dynamicAnchor" keywords are used to specify such
   fragments.  They are identifier keywords that can only be used to
   create plain name fragments.






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   The base URI to which the resulting fragment is appended is the
   canonical URI of the schema resource containing the "$anchor" or
   "$dynamicAnchor" in question.  As discussed in the previous section,
   this is either the nearest "$id" in the same or parent schema object,
   or the base URI for the document as determined according to RFC 3986.

   Separately from the usual usage of URIs, "$dynamicAnchor" indicates
   that the fragment is an extension point when used with the
   "$dynamicRef" keyword.  This low-level, advanced feature makes it
   easier to extend recursive schemas such as the meta-schemas, without
   imposing any particular semantics on that extension.  See the section
   on "$dynamicRef" (Section 5.2.1) for details.

   In most cases, the normal fragment behavior both suffices and is more
   intuitive.  Therefore it is RECOMMENDED that "$anchor" be used to
   create plain name fragments unless there is a clear need for
   "$dynamicAnchor".

   If present, the value of this keyword MUST be a string and MUST start
   with a letter ([A-Za-z]) or underscore ("_"), followed by any number
   of letters, digits ([0-9]), hyphens ("-"), underscores ("_"), and
   periods (".").  This matches the US-ASCII part of XML's NCName
   production, per [XMLNS].
   // Note that the anchor string does not include the "#" character, as
   // it is not a URI-reference.  An "$anchor": "foo" becomes the
   // fragment "#foo" when used in a URI.  See below for full examples.

   The effect of specifying the same fragment name multiple times within
   the same resource, using any combination of "$anchor" and/or
   "$dynamicAnchor", is undefined.  Implementations MAY raise an error
   if such usage is detected.

5.2.  Definitions and References

5.2.1.  "$ref" and "$dynamicRef"

   The "$ref" and "$dynamicRef" keywords are applicator keywords used to
   reference a schema.  Their results are the results of the referenced
   schema.
   // Note that this definition of how the results are determined means
   // that other keywords can appear alongside of "$ref" in the same
   // schema object.

   As the values of "$ref" and "$dynamicRef" are URI References, this
   allows the possibility to externalise or divide a schema across
   multiple files, and provides the ability to validate recursive
   structures through self-reference.




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   The resolved URI produced by these keywords is not necessarily a
   network locator, only an identifier.  Even if it is a network
   locator, implementations should refer to Section 12.1.2 about loading
   such schemas.

   The value of the "$ref" keyword MUST be a string which is a URI-
   Reference.  Resolved against the current URI base, it produces the
   URI of the schema to apply.  This resolution is safe to perform on
   schema load, as the process of evaluating an input cannot change how
   the reference resolves.

   The "$dynamicRef" keyword is an applicator that allows for deferring
   the full resolution until runtime, at which point it is resolved each
   time it is encountered while evaluating an input.

   Together with "$dynamicAnchor", "$dynamicRef" implements a
   cooperative extension mechanism that is primarily useful with
   recursive schemas (schemas that reference themselves).  Both the
   extension point and the runtime-determined extension target are
   defined with "$dynamicAnchor", and only exhibit runtime dynamic
   behavior when referenced with "$dynamicRef".

   The value of the "$dynamicRef" property MUST be a string which is a
   URI-Reference.  Resolved against the current URI base, it produces
   the URI used as the starting point for runtime resolution.  This
   initial resolution is safe to perform on schema load.

   If the initially resolved starting point URI includes a fragment that
   was created by the "$dynamicAnchor" keyword, the initial URI MUST be
   replaced by the URI (including the fragment) for the outermost schema
   resource in the dynamic scope (Section 13.1) that defines an
   identically named fragment with "$dynamicAnchor".

   Otherwise, its behavior is identical to "$ref", and no runtime
   resolution is needed.

   For a full example using these keyword, see Appendix C.
   // The difference between the hyper-schema meta-schema in pre-2019
   // drafts and an this draft dramatically demonstrates the utility of
   // these keywords.

5.2.2.  "$defs"

   The "$defs" keyword reserves a location for schema authors to inline
   re-usable JSON Schemas into a more general schema.  The keyword does
   not directly affect the validation result.





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   This keyword's value MUST be an object.  Each member value of this
   object MUST be a valid JSON Schema.

   As an example, here is a schema describing an array of positive
   integers, where the positive integer constraint is a subschema in
   "$defs":

   {
       "type": "array",
       "items": { "$ref": "#/$defs/positiveInteger" },
       "$defs": {
           "positiveInteger": {
               "type": "integer",
               "exclusiveMinimum": 0
           }
       }
   }

5.3.  "$comment"

   This keyword reserves a location for comments from schema authors to
   readers or maintainers of the schema.

   The value of this keyword MUST be a string.  Implementations MUST NOT
   present this string to end users.  Tools for editing schemas SHOULD
   support displaying and editing this keyword.  The value of this
   keyword MAY be used in debug or error output which is intended for
   developers making use of schemas.

   Schema vocabularies SHOULD allow "$comment" within any object
   containing vocabulary keywords.  Implementations MAY assume
   "$comment" is allowed unless the vocabulary specifically forbids it.
   Vocabularies MUST NOT specify any effect of "$comment" beyond what is
   described in this specification.

   Tools that translate other media types or programming languages to
   and from application/schema+json MAY choose to convert that media
   type or programming language's native comments to or from "$comment"
   values.  The behavior of such translation when both native comments
   and "$comment" properties are present is implementation-dependent.

   Implementations MAY strip "$comment" values at any point during
   processing.  In particular, this allows for shortening schemas when
   the size of deployed schemas is a concern.

   Implementations MUST NOT take any other action based on the presence,
   absence, or contents of "$comment" properties.  In particular, the
   value of "$comment" MUST NOT be collected as an annotation result.



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6.  Subschema keywords

   This section defines keywords that are RECOMMENDED for use as the
   basis of other vocabularies.

   Meta-schemas that do not use "$vocabulary" SHOULD be considered to
   require this vocabulary as if its URI were present with a value of
   true.

   The current URI for this vocabulary, known as the Applicator
   vocabulary, is:

   <https://json-schema.org/draft/2020-12/vocab/applicator>.

   The current URI for the corresponding meta-schema is:

   https://json-schema.org/draft/2020-12/meta/applicator (https://json-
   schema.org/draft/2020-12/meta/applicator).

6.1.  Keyword Independence

   Schema keywords typically operate independently, without affecting
   each other's outcomes.

   For schema author convenience, there are some exceptions among the
   keywords in this vocabulary:

   *  "additionalProperties", whose behavior is defined in terms of
      "properties" and "patternProperties"

   *  "items", whose behavior is defined in terms of "prefixItems"

   *  "contains", whose behavior is affected by the presence and value
      of "minContains", in the Validation vocabulary

6.2.  Keywords for Applying Subschemas in Place

   These keywords apply subschemas to the same location in the input as
   the parent schema is being applied.  They allow combining or
   modifying the subschema results in various ways.

   Subschemas of these keywords evaluate the input completely
   independently such that the results of one such subschema MUST NOT
   impact the results of sibling subschemas.  Therefore subschemas may
   be applied in any order.






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   Three of these keywords work together to implement conditional
   application of a subschema based on the outcome of another subschema.
   The fourth is a shortcut for a specific conditional case.

   "if", "then", and "else" MUST NOT interact with each other across
   subschema boundaries.  In other words, an "if" in one branch of an
   "allOf" MUST NOT have an impact on a "then" or "else" in another
   branch.

   There is no default behavior for "if", "then", or "else" when they
   are not present.  In particular, they MUST NOT be treated as if
   present with an empty schema, and when "if" is not present, both
   "then" and "else" MUST be entirely ignored.

6.2.1.  "allOf"

   This keyword's value MUST be a non-empty array.  Each item of the
   array MUST be a valid JSON Schema.

   An input validates successfully against this keyword if it validates
   successfully against all schemas defined by this keyword's value.

6.2.2.  "anyOf"

   This keyword's value MUST be a non-empty array.  Each item of the
   array MUST be a valid JSON Schema.

   An input validates successfully against this keyword if it validates
   successfully against at least one schema defined by this keyword's
   value.  Note that when annotations are being collected, all
   subschemas MUST be examined so that annotations are collected from
   each subschema that validates successfully.

6.2.3.  "oneOf"

   This keyword's value MUST be a non-empty array.  Each item of the
   array MUST be a valid JSON Schema.

   An input validates successfully against this keyword if it validates
   successfully against exactly one schema defined by this keyword's
   value.

6.2.4.  "not"

   This keyword's value MUST be a valid JSON Schema.

   An input is valid against this keyword if it fails to validate
   successfully against the schema defined by this keyword.



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6.2.5.  "if"

   This keyword's value MUST be a valid JSON Schema.

   This validation outcome of this keyword's subschema has no direct
   effect on the overall validation result.  Rather, it controls which
   of the "then" or "else" keywords are evaluated.

   Inputs that successfully validate against this keyword's subschema
   MUST also be valid against the subschema value of the "then" keyword,
   if present.

   Iputs that fail to validate against this keyword's subschema MUST
   also be valid against the subschema value of the "else" keyword, if
   present.

   If Section 13.8 are being collected, they are collected from this
   keyword's subschema in the usual way, including when the keyword is
   present without either "then" or "else".

6.2.6.  "then"

   This keyword's value MUST be a valid JSON Schema.

   When "if" is present, and the input successfully validates against
   its subschema, then validation succeeds against this keyword if the
   input also successfully validates against this keyword's subschema.

   This keyword has no effect when "if" is absent, or when the input
   fails to validate against its subschema.  Implementations MUST NOT
   evaluate the input against this keyword, for either validation or
   annotation collection purposes, in such cases.

6.2.7.  "else"

   This keyword's value MUST be a valid JSON Schema.

   When "if" is present, and the input fails to validate against its
   subschema, then validation succeeds against this keyword if the input
   successfully validates against this keyword's subschema.

   This keyword has no effect when "if" is absent, or when the input
   successfully validates against its subschema.  Implementations MUST
   NOT evaluate the input against this keyword, for either validation or
   annotation collection purposes, in such cases.






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6.2.8.  "dependentSchemas"

   This keyword specifies subschemas that are evaluated if the input is
   an object and contains a certain property.

   This keyword's value MUST be an object.  Each value in the object
   MUST be a valid JSON Schema.

   If the object key is a property in the instance, the entire instance
   must validate against the subschema.  Its use is dependent on the
   presence of the property.

   Omitting this keyword has the same behavior as an empty object.

6.3.  Keywords for Applying Subschemas to Arrays

   Each of these keywords defines a rule for applying its subschema(s)
   to array items, and combining their results.

6.3.1.  "prefixItems"

   The value of "prefixItems" MUST be a non-empty array of valid JSON
   Schemas.

   Validation succeeds if each element of the input validates against
   the schema at the same position, if any.  This keyword does not
   constrain the length of the array.  If the array is longer than this
   keyword's value, this keyword validates only the prefix of matching
   length.

   This keyword produces an annotation value which is the largest index
   to which this keyword applied a subschema.  The value MAY be a
   boolean true if a subschema was applied to every index of the
   instance, such as is produced by the "items" keyword.  This
   annotation affects the behavior of "items" and "unevaluatedItems".

   Omitting this keyword has the same assertion behavior as an empty
   array.

6.3.2.  "items"

   The value of "items" MUST be a valid JSON Schema.

   This keyword applies its subschema to all input elements at indexes
   greater than the length of the "prefixItems" array in the same schema
   object, as reported by the annotation result of that "prefixItems"
   keyword.  If no such annotation result exists, "items" applies its
   subschema to all input array elements.



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   // Note that the behavior of "items" without "prefixItems" is
   // identical to that of the schema form of "items" in prior drafts.
   // When "prefixItems" is present, the behavior of "items" is
   // identical to the former "additionalItems" keyword.

   If the "items" subschema is applied to any positions within the input
   array, it produces an annotation result of boolean true, indicating
   that all remaining array elements have been evaluated against this
   keyword's subschema.  This annotation affects the behavior of
   "unevaluatedItems" in the Unevaluated vocabulary.

   Omitting this keyword has the same assertion behavior as an empty
   schema.

   Implementations MAY choose to implement or optimize this keyword in
   another way that produces the same effect, such as by directly
   checking for the presence and size of a "prefixItems" array.
   Implementations that do not support annotation collection MUST do so.

6.3.3.  "contains"

   The value of this keyword MUST be a valid JSON Schema.

   An array input is valid against "contains" if the number of elements
   that are valid against its subschema is within the inclusive range of
   the minimum and (if any) maximum number of occurrences.

   The minimum and maximum numbers of occurrences are provided by the
   "minContains" and "maxContains" keywords, respectively, within the
   same schema object as "contains".  If "minContains" is absent, the
   minimum MUST be 1.  If "maxContains" is absent, the maximum MUST be
   unbounded.

   Implementations MAY implement the dependency on "minContains" and
   "maxContains" by inspecting their values rather than by reading
   annotations provided by those keywords.

   This keyword produces an annotation value which is an array of the
   indexes to which this keyword validates successfully when applying
   its subschema, in ascending order.  The value MAY be a boolean "true"
   if the subschema validates successfully when applied to every index
   of the instance.  The annotation MUST be present if the input array
   to which this keyword's schema applies is empty.

   This annotation affects the behavior of "unevaluatedItems" in the
   Unevaluated vocabulary.





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   The subschema MUST be applied to every array element even after the
   first match has been found, in order to collect annotations for use
   by other keywords.  This is to ensure that all possible annotations
   are collected.

6.4.  Keywords for Applying Subschemas to Objects

   Each of these keywords defines a rule for applying its subschema(s)
   to object properties and combining their results.

6.4.1.  "properties"

   The value of "properties" MUST be an object.  Each value of this
   object MUST be a valid JSON Schema.

   Validation succeeds if, for each name that appears in both the input
   and as a name within this keyword's value, the contents successfully
   validate against the corresponding schema.

   The annotation result of this keyword is the set of instance property
   names matched by this keyword.  This annotation affects the behavior
   of "additionalProperties" (in this vocabulary) and
   "unevaluatedProperties" in the Unevaluated vocabulary.

   Omitting this keyword has the same assertion behavior as an empty
   object.

6.4.2.  "patternProperties"

   The value of "patternProperties" MUST be an object.  Each property
   name of this object SHOULD be a valid regular expression, according
   to the ECMA-262 regular expression dialect.  Each property value of
   this object MUST be a valid JSON Schema.

   Validation succeeds if, for each input name that matches any regular
   expressions that appear as a property name in this keyword's value,
   the contents successfully validate against each schema that
   corresponds to a matching regular expression.  Recall: Regular
   expressions are not explicitly anchored.

   The annotation result of this keyword is the set of instance property
   names matched by this keyword.  This annotation affects the behavior
   of "additionalProperties" (in this vocabulary) and
   "unevaluatedProperties" (in the Unevaluated vocabulary).

   Omitting this keyword has the same assertion behavior as an empty
   object.




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6.4.3.  "additionalProperties"

   The value of "additionalProperties" MUST be a valid JSON Schema.

   The behavior of this keyword depends on the presence and annotation
   results of "properties" and "patternProperties" within the same
   schema object.  Validation with "additionalProperties" applies only
   to the child values of input names that do not appear in the
   annotation results of either "properties" or "patternProperties".

   For all such properties, validation succeeds if the contents validate
   against the "additionalProperties" schema.

   The annotation result of this keyword is the set of input property
   names validated by this keyword's subschema.  This annotation affects
   the behavior of "unevaluatedProperties" in the Unevaluated
   vocabulary.

   Omitting this keyword has the same assertion behavior as an empty
   schema.

   Implementations MAY choose to implement or optimize this keyword in
   another way that produces the same effect, such as by directly
   checking the names in "properties" and the patterns in
   "patternProperties" against the input property set.  Implementations
   that do not support annotation collection MUST do so.
   // In defining this option, it seems there is the potential for
   // ambiguity in the output format.  The ambiguity does not affect
   // validation results, but it does affect the resulting output
   // format.  The ambiguity allows for multiple valid output results
   // depending on whether annotations are used or a solution that
   // "produces the same effect" as draft-07.  It is understood that
   // annotations from failing schemas are dropped.  See our Decision
   // Record (https://github.com/json-schema-org/json-schema-
   // spec/tree/HEAD/adr/2022-04-08-cref-for-ambiguity-and-fix-later-gh-
   // spec-issue-1172.md) for further details.

6.4.4.  "propertyNames"

   The value of "propertyNames" MUST be a valid JSON Schema.

   If the input is an object, this keyword validates if every property
   name in the input validates against the provided schema.  Note the
   property name that the schema is testing will always be a string.

   Omitting this keyword has the same behavior as an empty schema.





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7.  Keywords for Unevaluated Locations

   The purpose of these keywords is to enable schema authors to apply
   subschemas to array items or object properties that have not been
   successfully evaluated against any dynamic-scope subschema of any
   adjacent keywords.

   These input items or properties may have been unsuccessfully
   evaluated against one or more adjacent keyword subschemas, such as
   when an assertion in a branch of an "anyOf" fails.  Such failed
   evaluations are not considered to contribute to whether or not the
   item or property has been evaluated.  Only successful evaluations are
   considered.

   If an item in an array or an object property is "successfully
   evaluated", it is logically considered to be valid in terms of the
   representation of the object or array that's expected.  For example
   if a subschema represents a car, which requires between 2-4 wheels,
   and the value of "wheels" is 6, the input object is not "evaluated"
   to be a car, and the "wheels" property is considered "unevaluated
   (successfully as a known thing)", and does not retain any
   annotations.

   Recall that adjacent keywords are keywords within the same schema
   object, and that the dynamic-scope subschemas include reference
   targets as well as lexical subschemas.

   The behavior of these keywords depend on the annotation results of
   adjacent keywords that apply to the input location being validated.

   Meta-schemas that do not use "$vocabulary" SHOULD be considered to
   require this vocabulary as if its URI were present with a value of
   true.

   The current URI for this vocabulary, known as the Unevaluated
   Applicator vocabulary, is:

   <https://json-schema.org/draft/2020-12/vocab/unevaluated>.

   The current URI for the corresponding meta-schema is:

   https://json-schema.org/draft/2020-12/meta/unevaluated (https://json-
   schema.org/draft/2020-12/meta/unevaluated).








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7.1.  Keyword Independence

   Schema keywords typically operate independently, without affecting
   each other's outcomes.  However, the keywords in this vocabulary are
   notable exceptions:

   *  "unevaluatedItems", whose behavior is defined in terms of
      annotations from "prefixItems", "items", "contains", and itself

   *  "unevaluatedProperties", whose behavior is defined in terms of
      annotations from "properties", "patternProperties",
      "additionalProperties" and itself

7.2.  "unevaluatedItems"

   The value of "unevaluatedItems" MUST be a valid JSON Schema.

   The behavior of this keyword depends on the annotation results of
   adjacent keywords that apply to the input location being validated.
   Specifically, the annotations from "prefixItems", "items", and
   "contains", which can come from those keywords when they are adjacent
   to the "unevaluatedItems" keyword.  Those three annotations, as well
   as "unevaluatedItems", can also result from any and all adjacent
   in-place applicator (Section 6.2) keywords.  This includes but is not
   limited to the in-place applicators defined in this document.

   If no relevant annotations are present, the "unevaluatedItems"
   subschema MUST be applied to all locations in the array.  If a
   boolean true value is present from any of the relevant annotations,
   "unevaluatedItems" MUST be ignored.  Otherwise, the subschema MUST be
   applied to any index greater than the largest annotation value for
   "prefixItems", which does not appear in any annotation value for
   "contains".

   This means that "prefixItems", "items", "contains", and all in-place
   applicators MUST be evaluated before this keyword can be evaluated.
   Authors of extension keywords MUST NOT define an in-place applicator
   that would need to be evaluated after this keyword.

   If the "unevaluatedItems" subschema is applied to any positions
   within the input array, it produces an annotation result of boolean
   true, analogous to the behavior of "items".  This annotation affects
   the behavior of "unevaluatedItems" in parent schemas.

   Omitting this keyword has the same assertion behavior as an empty
   schema.





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7.3.  "unevaluatedProperties"

   The value of "unevaluatedProperties" MUST be a valid JSON Schema.

   The behavior of this keyword depends on the annotation results of
   adjacent keywords that apply to the input location being validated.
   Specifically, the annotations from "properties", "patternProperties",
   and "additionalProperties", which can come from those keywords when
   they are adjacent to the "unevaluatedProperties" keyword.  Those
   three annotations, as well as "unevaluatedProperties", can also
   result from any and all adjacent in-place applicator (Section 6.2)
   keywords.  This includes but is not limited to the in-place
   applicators defined in this document.

   Validation with "unevaluatedProperties" applies only to the child
   values of input names that do not appear in the "properties",
   "patternProperties", "additionalProperties", or
   "unevaluatedProperties" annotation results that apply to the instance
   location being validated.

   For all such properties, validation succeeds if the contents validate
   against the "unevaluatedProperties" schema.

   This means that "properties", "patternProperties",
   "additionalProperties", and all in-place applicators MUST be
   evaluated before this keyword can be evaluated.  Authors of extension
   keywords MUST NOT define an in-place applicator that would need to be
   evaluated after this keyword.

   The annotation result of this keyword is the set of instance property
   names validated by this keyword's subschema.  This annotation affects
   the behavior of "unevaluatedProperties" in parent schemas.

   Omitting this keyword has the same assertion behavior as an empty
   schema.

8.  Keywords for Structural Validation

   Validation keywords in a schema impose requirements for successful
   validation of an input.  These keywords are all assertions without
   any annotation behavior.

   Meta-schemas that do not use "$vocabulary" SHOULD be considered to
   require this vocabulary as if its URI were present with a value of
   true.

   The current URI for this vocabulary, known as the Validation
   vocabulary, is:



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   <https://json-schema.org/draft/2020-12/vocab/validation>.

   The current URI for the corresponding meta-schema is:

   https://json-schema.org/draft/2020-12/meta/validation (https://json-
   schema.org/draft/2020-12/meta/validation).

8.1.  Validation Keywords for Any Instance Type

8.1.1.  "type"

   The value of this keyword MUST be either a string or an array.  If it
   is an array, elements of the array MUST be strings and MUST be
   unique.

   String values MUST be one of the six primitive types ("null",
   "boolean", "object", "array", "number", or "string"), or "integer"
   which matches any number with a zero fractional part.

   If the value of "type" is a string, then an input validates
   successfully if its type matches the type represented by the value of
   the string.

   If the value of "type" is an array, then an input validates
   successfully if its type matches any of the types indicated by the
   strings in the array.

8.1.2.  "enum"

   The value of this keyword MUST be an array.  This array SHOULD have
   at least one element.  Elements in the array SHOULD be unique.

   An input validates successfully against this keyword if its value is
   equal to one of the elements in this keyword's array value.

   Elements in the array might be of any type, including null.

8.1.3.  "const"

   The value of this keyword MAY be of any type, including null.

   Use of this keyword is functionally equivalent to an Section 8.1.2
   with a single value.

   An input validates successfully against this keyword if its value is
   equal to the value of the keyword.





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8.2.  Validation Keywords for Numeric Inputs (number and integer)

8.2.1.  "multipleOf"

   The value of "multipleOf" MUST be a number, strictly greater than 0.

   A numeric input value is valid only if division by this keyword's
   value results in an integer.

8.2.2.  "maximum"

   The value of "maximum" MUST be a number, representing an inclusive
   upper limit for a numeric input value.

   If the input value is a number, then this keyword validates only if
   the input value is less than or exactly equal to "maximum".

8.2.3.  "exclusiveMaximum"

   The value of "exclusiveMaximum" MUST be a number, representing an
   exclusive upper limit for a numeric input value.

   If the input value is a number, then it is valid only if it has a
   value strictly less than (not equal to) "exclusiveMaximum".

8.2.4.  "minimum"

   The value of "minimum" MUST be a number, representing an inclusive
   lower limit for a numeric input value.

   If the input value is a number, then it is valid only if it has a
   value that is greater than or exactly equal to "minimum".

8.2.5.  "exclusiveMinimum"

   The value of "exclusiveMinimum" MUST be a number, representing an
   exclusive lower limit for a numeric input value.

   If the input value is a number, then it is valid only if it has a
   value strictly greater than (not equal to) "exclusiveMinimum".

8.3.  Validation Keywords for Strings

8.3.1.  "maxLength"

   The value of this keyword MUST be a non-negative integer.





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   A string input value is valid against this keyword if its length is
   less than, or equal to, the value of this keyword.

   The length of a string input value is defined as the number of its
   characters as defined by [RFC8259].

8.3.2.  "minLength"

   The value of this keyword MUST be a non-negative integer.

   A string input value is valid against this keyword if its length is
   greater than, or equal to, the value of this keyword.

   The length of a string input value is defined as the number of its
   characters as defined by [RFC8259].

   Omitting this keyword has the same behavior as a value of 0.

8.3.3.  "pattern"

   The value of this keyword MUST be a string.  This string SHOULD be a
   valid regular expression, according to the ECMA-262 regular
   expression dialect.

   A string input value is considered valid if the regular expression
   matches the input value successfully.  Recall: regular expressions
   are not implicitly anchored.

8.4.  Validation Keywords for Arrays

8.4.1.  "maxItems"

   The value of this keyword MUST be a non-negative integer.

   An array input value is valid against "maxItems" if its size is less
   than, or equal to, the value of this keyword.

8.4.2.  "minItems"

   The value of this keyword MUST be a non-negative integer.

   An array input value is valid against "minItems" if its size is
   greater than, or equal to, the value of this keyword.

   Omitting this keyword has the same behavior as a value of 0.






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8.4.3.  "uniqueItems"

   The value of this keyword MUST be a boolean.

   If this keyword has boolean value false, the input array validates
   successfully.  If it has boolean value true, the input array
   validates successfully if all of its elements are unique.

   Omitting this keyword has the same behavior as a value of false.

8.4.4.  "maxContains"

   The value of this keyword MUST be a non-negative integer.

   Validation MUST always succeed against this keyword; its validation
   effect is to modify the behavior of "contains" within the same schema
   object, as described in that keyword's section.

   This keyword behaves as an annotation, which MAY be used by
   "Section 6.3.3".

8.4.5.  "minContains"

   The value of this keyword MUST be a non-negative integer.

   Validation MUST always succeed against this keyword; its validation
   effect is to modify the behavior of "contains" within the same schema
   object, as described in that keyword's section.

   This keyword behaves as an annotation, which MAY be used by
   "Section 6.3.3".

   Omitting this keyword has the same behavior as a value of 1.  Per
   Section 13.3, omitted keywords MUST NOT produce annotation results.
   However, as described in the section for "contains", the absence of
   this keyword's annotation causes "contains" to assume a value of 1.

8.5.  Validation Keywords for Objects

8.5.1.  "maxProperties"

   The value of this keyword MUST be a non-negative integer.

   An object is valid against "maxProperties" if its number of
   properties is less than, or equal to, the value of this keyword.






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8.5.2.  "minProperties"

   The value of this keyword MUST be a non-negative integer.

   An object is valid against "minProperties" if its number of
   properties is greater than, or equal to, the value of this keyword.

   Omitting this keyword has the same behavior as a value of 0.

8.5.3.  "required"

   The value of this keyword MUST be an array.  Elements of this array,
   if any, MUST be strings, and MUST be unique.

   An object is valid against this keyword if every item in the array is
   the name of a property in the object.

   Omitting this keyword has the same behavior as an empty array.

8.5.4.  "dependentRequired"

   The value of this keyword MUST be an object.  Properties in this
   object, if any, MUST be arrays.  Elements in each array, if any, MUST
   be strings, and MUST be unique.

   This keyword specifies properties that are required if a specific
   other property is present.  Their requirement is dependent on the
   presence of the other property.

   Validation succeeds if, for each name that appears in both the input
   object and as a name within this keyword's value, every item in the
   corresponding array is also the name of a property in the input
   object.

   Omitting this keyword has the same behavior as an empty object.

9.  Vocabularies for Semantic Content With "format"

9.1.  Foreword

   Structural validation alone may be insufficient to allow an
   application to correctly utilize certain values.  The "format"
   annotation keyword is defined to allow schema authors to convey
   semantic information for a fixed subset of values which are
   accurately described by authoritative resources, be they RFCs or
   other external specifications.





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   The value of this keyword is called a format attribute.  It MUST be a
   string.  A format attribute can generally only validate a given set
   of input types.  If the type of the input is not in this set,
   validation for this format attribute and input SHOULD succeed.  All
   format attributes defined in this section apply to strings, but a
   format attribute can be specified to apply to any input type in the
   instance data model (Section 4.2).
   // Note that the "type" keyword in this specification defines an
   // "integer" type which is not part of the data model.  Therefore a
   // format attribute can be limited to numbers, but not specifically
   // to integers.  However, a numeric format can be used alongside the
   // "type" keyword with a value of "integer", or could be explicitly
   // defined to always pass if the number is not an integer, which
   // produces essentially the same behavior as only applying to
   // integers.

   The current URI for this vocabulary, known as the Format-Annotation
   vocabulary, is:

   <https://json-schema.org/draft/2020-12/vocab/format-annotation>.

   The current URI for the corresponding meta-schema is:

   https://json-schema.org/draft/2020-12/meta/format-annotation
   (https://json-schema.org/draft/2020-12/meta/format-annotation).

   Implementing support for this vocabulary is REQUIRED.

   In addition to the Format-Annotation vocabulary, a secondary
   vocabulary is available for custom meta-schemas that defines "format"
   as an assertion.  The URI for the Format-Assertion vocabulary, is:

   <https://json-schema.org/draft/2020-12/vocab/format-assertion>.

   The current URI for the corresponding meta-schema is:

   https://json-schema.org/draft/2020-12/meta/format-assertion
   (https://json-schema.org/draft/2020-12/meta/format-assertion).

   Implementing support for the Format-Assertion vocabulary is OPTIONAL.

   Specifying both the Format-Annotation and the Format-Assertion
   vocabularies is functionally equivalent to specifying only the
   Format-Assertion vocabulary since its requirements are a superset of
   the Format-Annotation vocabulary.






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9.2.  Implementation Requirements

   The "format" keyword functions as defined by the vocabulary which is
   referenced.

9.2.1.  Format-Annotation Vocabulary

   The value of format MUST be collected as an annotation, if the
   implementation supports annotation collection.  This enables
   application-level validation when schema validation is unavailable or
   inadequate.

   Implementations MAY still treat "format" as an assertion in addition
   to an annotation and attempt to validate the value's conformance to
   the specified semantics.  The implementation MUST provide options to
   enable and disable such evaluation and MUST be disabled by default.
   Implementations SHOULD document their level of support for such
   validation.
   // Specifying the Format-Annotation vocabulary and enabling
   // validation in an implementation should not be viewed as being
   // equivalent to specifying the Format-Assertion vocabulary since
   // implementations are not required to provide full validation
   // support when the Format-Assertion vocabulary is not specified.

   When the implementation is configured for assertion behavior, it:

   *  SHOULD provide an implementation-specific best effort validation
      for each format attribute defined below;

   *  MAY choose to implement validation of any or all format attributes
      as a no-op by always producing a validation result of true;


   // This matches the current reality of implementations, which provide
   // widely varying levels of validation, including no validation at
   // all, for some or all format attributes.  It is also designed to
   // encourage relying only on the annotation behavior and performing
   // semantic validation in the application, which is the recommended
   // best practice.

9.2.2.  Format-Assertion Vocabulary

   When the Format-Assertion vocabulary is declared with a value of
   true, implementations MUST provide full validation support for all of
   the formats defined by this specificaion.  Implementations that
   cannot provide full validation support MUST refuse to process the
   schema.




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   An implementation that supports the Format-Assertion vocabulary:

   *  MUST still collect "format" as an annotation if the implementation
      supports annotation collection;

   *  MUST evaluate "format" as an assertion;

   *  MUST implement syntactic validation for all format attributes
      defined in this specification, and for any additional format
      attributes that it recognizes, such that there exist possible
      input values of the correct type that will fail validation.

   The requirement for minimal validation of format attributes is
   intentionally vague and permissive, due to the complexity involved in
   many of the attributes.  Note in particular that the requirement is
   limited to syntactic checking; it is not to be expected that an
   implementation would send an email, attempt to connect to a URL, or
   otherwise check the existence of an entity identified by a format
   instance.
   // The expectation is that for simple formats such as date-time,
   // syntactic validation will be thorough.  For a complex format such
   // as email addresses, which are the amalgamation of various
   // standards and numerous adjustments over time, with obscure and/or
   // obsolete rules that may or may not be restricted by other
   // applications making use of the value, a minimal validation is
   // sufficient.  For example, an input string that does not contain an
   // "@" is clearly not a valid email address, and an "email" or
   // "hostname" containing characters outside of 7-bit ASCII is
   // likewise clearly invalid.

   It is RECOMMENDED that implementations use a common parsing library
   for each format, or a well-known regular expression.  Implementations
   SHOULD clearly document how and to what degree each format attribute
   is validated.

   The standard core and validation meta-schema includes this vocabulary
   in its "$vocabulary" keyword with a value of false, since by default
   implementations are not required to support this keyword as an
   assertion.  Supporting the format vocabulary with a value of true is
   understood to greatly increase code size and in some cases execution
   time, and will not be appropriate for all implementations.










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9.2.3.  Custom format attributes

   Implementations MAY support custom format attributes.  Save for
   agreement between parties, schema authors SHALL NOT expect a peer
   implementation to support such custom format attributes.  An
   implementation MUST NOT fail to collect unknown formats as
   annotations.  When the Format-Assertion vocabulary is specified,
   implementations MUST fail upon encountering unknown formats.

   Vocabularies do not support specifically declaring different value
   sets for keywords.  Due to this limitation, and the historically
   uneven implementation of this keyword, it is RECOMMENDED to define
   additional keywords in a custom vocabulary rather than additional
   format attributes if interoperability is desired.

9.3.  Defined Formats

9.3.1.  Dates, Times, and Duration

   These attributes apply to string inputs.

   Date and time format names are derived from [RFC3339], Section 5.6.
   The duration format is from the ISO 8601 ABNF as given in Appendix A
   of RFC 3339.

   Implementations supporting formats SHOULD implement support for the
   following attributes:

9.3.1.1.  "date-time"

   A string input is valid against this attribute if it is a valid
   representation according to the "date-time' ABNF rule (referenced
   above).

9.3.1.2.  "date"

   A string input is valid against this attribute if it is a valid
   representation according to the "full-date" ABNF rule (referenced
   above).

9.3.1.3.  "time"

   A string input is valid against this attribute if it is a valid
   representation according to the "full-time" ABNF rule (referenced
   above).






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9.3.1.4.  "duration"

   A string input is valid against this attribute if it is a valid
   representation according to the "duration" ABNF rule (referenced
   above).

9.3.1.5.  Additional RFC3339 Formats

   Implementations MAY support additional attributes using the other
   format names defined anywhere in that RFC.  If "full-date" or "full-
   time" are implemented, the corresponding short form ("date" or "time"
   respectively) MUST be implemented, and MUST behave identically.
   Implementations SHOULD NOT define extension attributes with any name
   matching an RFC 3339 format unless it validates according to the
   rules of that format.
   // There is not currently consensus on the need for supporting all
   // RFC 3339 formats, so this approach of reserving the namespace will
   // encourage experimentation without committing to the entire set.
   // Either the format implementation requirements will become more
   // flexible in general, or these will likely either be promoted to
   // fully specified attributes or dropped.

9.3.2.  Email Addresses

   These attributes apply to string inputs.

   A string input is valid against these attributes if it is a valid
   Internet email address as follows:

9.3.2.1.  "email"

   As defined by the "Mailbox" ABNF rule in [RFC5321], Section 4.1.2.

9.3.2.2.  "idn-email"

   As defined by the extended "Mailbox" ABNF rule in [RFC6531],
   Section 3.3.

   Note that all strings valid against the "email" attribute are also
   valid against the "idn-email" attribute.

9.3.3.  Hostnames

   These attributes apply to string inputs.

   A string input is valid against these attributes if it is a valid
   representation for an Internet hostname as follows:




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9.3.3.1.  "hostname"

   As defined by [RFC1123], Section 2.1, including host names produced
   using the Punycode algorithm specified in [RFC5891], Section 4.4.

9.3.3.2.  "idn-hostname"

   As defined by either RFC 1123 as for hostname, or an
   internationalized hostname as defined by [RFC5890], Section 2.3.2.3.

   Note that all strings valid against the "hostname" attribute are also
   valid against the "idn-hostname" attribute.

9.3.4.  IP Addresses

   These attributes apply to string inputs.

   A string input is valid against these attributes if it is a valid
   representation of an IP address as follows:

9.3.4.1.  "ipv4"

   An IPv4 address according to the "dotted-quad" ABNF syntax as defined
   in [RFC2673], Section 3.2.

9.3.4.2.  "ipv6"

   An IPv6 address as defined in [RFC4291], Section 2.2.

9.3.5.  Resource Identifiers

   These attributes apply to string inputs.

9.3.5.1.  "uri"

   A string input is valid against this attribute if it is a valid URI,
   according to [RFC3986], Section 3.

9.3.5.2.  "uri-reference"

   A string input is valid against this attribute if it is a valid URI
   Reference (either a URI or a relative-reference), according to
   [RFC3986], Section 4.

9.3.5.3.  "iri"

   A string input is valid against this attribute if it is a valid IRI,
   according to [RFC3987], Section 2.2.



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9.3.5.4.  "iri-reference"

   A string input is valid against this attribute if it is a valid IRI
   Reference (either an IRI or a relative-reference), according to
   [RFC3987], Section 2.2.

9.3.5.5.  "uuid"

   A string input is valid against this attribute if it is a valid
   string representation of a UUID, according to [RFC4122].

   Note that all valid URIs are valid IRIs, and all valid URI References
   are also valid IRI References.

   Note also that the "uuid" format is for plain UUIDs, not UUIDs in
   URNs.  An example is "f81d4fae-7dec-11d0-a765-00a0c91e6bf6".  For
   UUIDs as URNs, use the "uri" format, with a "pattern" regular
   expression of "^urn:uuid:" to indicate the URI scheme and URN
   namespace.

9.3.6.  Templates

9.3.6.1.  "uri-template"

   This attribute applies to string inputs.

   A string input is valid against this attribute if it is a valid URI
   Template (of any level), according to [RFC6570].

   Note that URI Templates may be used for IRIs; there is no separate
   IRI Template specification.

9.3.7.  JSON Pointers

   These attributes apply to string inputs.

   To allow for both regular and relative JSON Pointers, use "anyOf" or
   "oneOf" to indicate support for either format.

9.3.7.1.  "json-pointer"

   A string input is valid against this attribute if it is a valid JSON
   string representation of a JSON Pointer, according to [RFC6901],
   Section 5.







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9.3.7.2.  "relative-json-pointer"

   A string input is valid against this attribute if it is a valid
   [I-D.hha-relative-json-pointer].

9.3.8.  Expressions

9.3.8.1.  "regex"

   This attribute applies to string inputs.

   A regular expression, which SHOULD be valid according to the
   [ECMA262] regular expression dialect.

   Implementations that validate formats MUST accept at least the subset
   of ECMA-262 defined in Regular Expressions (Section 9.3.8.1) section
   of this specification, and SHOULD accept all valid ECMA-262
   expressions.

10.  A Vocabulary for the Contents of String-Encoded Data

10.1.  Foreword

   Annotations defined in this section indicate that an instance
   contains non-JSON data encoded in a JSON string.

   These properties provide additional information required to interpret
   JSON data as rich multimedia documents.  They describe the type of
   content, how it is encoded, and/or how it may be validated.  They do
   not function as validation assertions; a malformed string-encoded
   document MUST NOT cause the containing instance to be considered
   invalid.

   Meta-schemas that do not use "$vocabulary" SHOULD be considered to
   require this vocabulary as if its URI were present with a value of
   true.

   The current URI for this vocabulary, known as the Content vocabulary,
   is:

   <https://json-schema.org/draft/2020-12/vocab/content>.

   The current URI for the corresponding meta-schema is:

   https://json-schema.org/draft/2020-12/meta/content (https://json-
   schema.org/draft/2020-12/meta/content).





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10.2.  Implementation Requirements

   Due to security and performance concerns, as well as the open-ended
   nature of possible content types, implementations MUST NOT
   automatically decode, parse, and/or validate the string contents by
   default.  This additionally supports the use case of embedded
   documents intended for processing by a different consumer than that
   which processed the containing document.

   All keywords in this section apply only to strings, and have no
   effect on other data types.

   Implementations MAY offer the ability to decode, parse, and/or
   validate the string contents automatically.  However, it MUST NOT
   perform these operations by default, and MUST provide the validation
   result of each string-encoded document separately from the enclosing
   document.  This process SHOULD be equivalent to fully evaluating the
   input against the original schema, followed by using the annotations
   to decode, parse, and/or validate each string-encoded document.
   // For now, the exact mechanism of performing and returning parsed
   // data and/or validation results from such an automatic decoding,
   // parsing, and validating feature is left unspecified.  Should such
   // a feature prove popular, it may be specified more thoroughly in a
   // future draft.

   See also the Security Considerations (Section 16) sections for
   possible vulnerabilities introduced by automatically processing
   inputs according to these keywords.

10.3.  "contentEncoding"

   If the input value is a string, this property defines that the string
   SHOULD be interpreted as encoded binary data and decoded using the
   encoding named by this property.

   Possible values indicating base 16, 32, and 64 encodings with several
   variations are listed in [RFC4648].  Additionally, sections 6.7 and
   6.8 of [RFC2045] provide encodings used in MIME.  This keyword is
   derived from MIME's Content-Transfer-Encoding header, which was
   designed to map binary data into ASCII characters.  It is not related
   to HTTP's Content-Encoding header, which is used to encode (e.g.
   compress or encrypt) the content of HTTP request and responses.









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   As "base64" is defined in both RFCs, the definition from RFC 4648
   SHOULD be assumed unless the string is specifically intended for use
   in a MIME context.  Note that all of these encodings result in
   strings consisting only of 7-bit ASCII characters.  Therefore, this
   keyword has no meaning for strings containing characters outside of
   that range.

   If this keyword is absent, but "contentMediaType" is present, this
   indicates that the encoding is the identity encoding, meaning that no
   transformation was needed in order to represent the content in a
   UTF-8 string.

   The value of this property MUST be a string.

10.4.  "contentMediaType"

   If the input value is a string, this property indicates the media
   type of the contents of the string.  If "contentEncoding" is present,
   this property describes the decoded string.

   The value of this property MUST be a string, which MUST be a media
   type, as defined by [RFC2046].

10.5.  "contentSchema"

   If the input value is a string, and if "contentMediaType" is present,
   this property contains a schema which describes the structure of the
   string.

   This keyword MAY be used with any media type that can be mapped into
   JSON Schema's data model.

   The value of this property MUST be a valid JSON schema.  It SHOULD be
   ignored if "contentMediaType" is not present.

10.6.  Example

   Here is an example schema, illustrating the use of "contentEncoding"
   and "contentMediaType":

   {
       "type": "string",
       "contentEncoding": "base64",
       "contentMediaType": "image/png"
   }

   Instances described by this schema are expected to be strings, and
   their values should be interpretable as base64-encoded PNG images.



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   Another example:

   {
       "type": "string",
       "contentMediaType": "text/html"
   }

   Instances described by this schema are expected to be strings
   containing HTML, using whatever character set the JSON string was
   decoded into.  Per [RFC8259], Section 8.1, outside of an entirely
   closed system, this MUST be UTF-8.

   This example describes a JWT that is MACed using the HMAC SHA-256
   algorithm, and requires the "iss" and "exp" fields in its claim set.

   {
       "type": "string",
       "contentMediaType": "application/jwt",
       "contentSchema": {
           "type": "array",
           "minItems": 2,
           "prefixItems": [
               {
                   "const": {
                       "typ": "JWT",
                       "alg": "HS256"
                   }
               },
               {
                   "type": "object",
                   "required": ["iss", "exp"],
                   "properties": {
                       "iss": {"type": "string"},
                       "exp": {"type": "integer"}
                   }
               }
           ]
       }
   }

   Note that "contentEncoding" does not appear.  While the "application/
   jwt" media type makes use of base64url encoding, that is defined by
   the media type, which determines how the JWT string is decoded into a
   list of two JSON data structures: first the header, and then the
   payload.  Since the JWT media type ensures that the JWT can be
   represented in a JSON string, there is no need for further encoding
   or decoding.




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11.  A Vocabulary for Basic Meta-Data Annotations

   These general-purpose annotation keywords provide commonly used
   information for documentation and user interface display purposes.
   They are not intended to form a comprehensive set of features.
   Rather, additional vocabularies can be defined for more complex
   annotation-based applications.

   Meta-schemas that do not use "$vocabulary" SHOULD be considered to
   require this vocabulary as if its URI were present with a value of
   true.

   The current URI for this vocabulary, known as the Meta-Data
   vocabulary, is:

   <https://json-schema.org/draft/2020-12/vocab/meta-data>.

   The current URI for the corresponding meta-schema is:

   https://json-schema.org/draft/2020-12/meta/meta-data (https://json-
   schema.org/draft/2020-12/meta/meta-data).

11.1.  "title" and "description"

   The value of both of these keywords MUST be a string.

   Both of these keywords can be used to decorate a user interface with
   information about the data produced by this user interface.  A title
   will preferably be short, whereas a description will provide
   explanation about the purpose of the instance described by this
   schema.

11.2.  "default"

   There are no restrictions placed on the value of this keyword.  When
   multiple occurrences of this keyword are applicable to a single sub-
   instance, implementations SHOULD remove duplicates.

   This keyword can be used to supply a default JSON value associated
   with a particular schema.  It is RECOMMENDED that a default value be
   valid against the associated schema.

11.3.  "deprecated"

   The value of this keyword MUST be a boolean.  When multiple
   occurrences of this keyword are applicable to a single sub-instance,
   applications SHOULD consider the instance location to be deprecated
   if any occurrence specifies a true value.



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   If "deprecated" has a value of boolean true, it indicates that
   applications SHOULD refrain from usage of the declared property.  It
   MAY mean the property is going to be removed in the future.

   A root schema containing "deprecated" with a value of true indicates
   that the entire resource being described MAY be removed in the
   future.

   The "deprecated" keyword applies to each instance location to which
   the schema object containing the keyword successfully applies.  This
   can result in scenarios where every array item or object property is
   deprecated even though the containing array or object is not.

   Omitting this keyword has the same behavior as a value of false.

11.4.  "readOnly" and "writeOnly"

   The value of these keywords MUST be a boolean.  When multiple
   occurrences of these keywords are applicable to a single sub-
   instance, the resulting behavior SHOULD be as for a true value if any
   occurrence specifies a true value, and SHOULD be as for a false value
   otherwise.

   If "readOnly" has a value of boolean true, it indicates that the
   value of the instance is managed exclusively by the owning authority,
   and attempts by an application to modify the value of this property
   are expected to be ignored or rejected by that owning authority.

   An instance document that is marked as "readOnly" for the entire
   document MAY be ignored if sent to the owning authority, or MAY
   result in an error, at the authority's discretion.

   If "writeOnly" has a value of boolean true, it indicates that the
   value is never present when the instance is retrieved from the owning
   authority.  It can be present when sent to the owning authority to
   update or create the document (or the resource it represents), but it
   will not be included in any updated or newly created version of the
   instance.

   An instance document that is marked as "writeOnly" for the entire
   document MAY be returned as a blank document of some sort, or MAY
   produce an error upon retrieval, or have the retrieval request
   ignored, at the authority's discretion.

   For example, "readOnly" would be used to mark a database-generated
   serial number as read-only, while "writeOnly" would be used to mark a
   password input field.




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   These keywords can be used to assist in user interface instance
   generation.  In particular, an application MAY choose to use a widget
   that hides input values as they are typed for write-only fields.

   Omitting these keywords has the same behavior as values of false.

11.5.  "examples"

   The value of this keyword MUST be an array.  There are no
   restrictions placed on the values within the array.  When multiple
   occurrences of this keyword are applicable to a single sub-instance,
   implementations MUST provide a flat array of all values rather than
   an array of arrays.

   This keyword can be used to provide sample JSON values associated
   with a particular schema, for the purpose of illustrating usage.  It
   is RECOMMENDED that these values be valid against the associated
   schema.

   Implementations MAY use the value(s) of "default", if present, as an
   additional example.  If "examples" is absent, "default" MAY still be
   used in this manner.

12.  Loading and Processing Schemas

12.1.  Loading a Schema

12.1.1.  Initial Base URI

   [RFC3986], Section 5.1 defines how to determine the default base URI
   of a document.

   Informatively, the initial base URI of a schema is the URI at which
   it was found, whether that was a network location, a local
   filesystem, or any other situation identifiable by a URI of any known
   scheme.

   If a schema document defines no explicit base URI with "$id"
   (embedded in content), the base URI is that determined per [RFC3986],
   Section 5.

   If no source is known, or no URI scheme is known for the source, a
   suitable implementation-specific default URI MAY be used as described
   in [RFC3986], Section 5.1.4.  It is RECOMMENDED that implementations
   document any default base URI that they assume.






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   If a schema object is embedded in a document of another media type,
   then the initial base URI is determined according to the rules of
   that media type.

   Unless the "$id" keyword described in an earlier section is present
   in the root schema, this base URI SHOULD be considered the canonical
   URI of the schema document's root schema resource.

12.1.2.  Loading a referenced schema

   Although it's impossible to cover all use cases, we start by assuming
   that an implementation given a schema with references to other
   schemas not in the same document can be given instructions about
   those other documents, and the implementation therefore SHOULD NOT
   automatically dereference network locations or search the network for
   schemas not already loaded in.

   What should implementations do when the referenced schema is not
   known?  The implementation could have error messages, flags or UX to
   explicitly get instructions to fetch a schema or to signal that it
   should be configured differently.  The examples from HTTP of same-
   origin policies would seem relevant here too, but such a feature has
   not yet been defined for JSON Schema.

   Some use cases may involve schema definitions that regularly are
   extended or updated by reference.  For example, a service hosting an
   evolving API might include documentation and requirements via JSON
   schemas, and the schemas might be intended for dynamic fetching and
   inclusion of sub-schemas, so placing an absolute requirement of pre-
   loading schema documents is not feasible.

   When schemas are downloaded, for example by a generic user-agent that
   does not know until runtime which schemas to download, see Usage for
   Hypermedia (Section 12.5).

   Implementations SHOULD be able to associate arbitrary URIs with an
   arbitrary schema and/or automatically associate a schema's "$id"-
   given URI, depending on the trust that the implementation has in the
   schema.  Such URIs and schemas can be supplied to an implementation
   prior to processing instances, or may be noted within a schema
   document as it is processed, producing associations as shown in
   Appendix A.

   A schema MAY (and likely will) have multiple URIs, but there is no
   way for a URI to identify more than one schema.  When multiple
   schemas try to identify as the same URI, an implementation SHOULD
   raise an error condition.




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12.1.3.  Detecting a Meta-Schema

   Implementations MUST recognize a schema as a meta-schema if it is
   being examined because it was identified as such by another schema's
   "$schema" keyword.  This means that a single schema document might
   sometimes be considered a regular schema, and other times be
   considered a meta-schema.

   In the case of examining a schema which is its own meta-schema, when
   an implementation begins processing it as a regular schema, it is
   processed under those rules.  However, when loaded a second time as a
   result of checking its own "$schema" value, it is treated as a meta-
   schema.  So the same document is processed both ways in the course of
   one session.

   Implementations MAY allow a schema to be explicitly passed as a meta-
   schema, for implementation-specific purposes, such as pre-loading a
   commonly used meta-schema and checking its vocabulary support
   requirements up front.  Meta-schema authors MUST NOT expect such
   features to be interoperable across implementations.

12.2.  Dereferencing

   Schemas can be identified by any URI that has been given to them,
   including a JSON Pointer or their URI given directly by "$id".  In
   all cases, dereferencing a "$ref" reference involves first resolving
   its value as a URI reference against the current base URI per
   [RFC3986].

   If the resulting URI identifies a schema within the current document,
   or within another schema document that has been made available to the
   implementation, then that schema SHOULD be used automatically.

   For example, consider this schema:

















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   {
       "$id": "https://example.net/root.json",
       "items": {
           "type": "array",
           "items": { "$ref": "#item" }
       },
       "$defs": {
           "single": {
               "$anchor": "item",
               "type": "object",
               "additionalProperties": { "$ref": "other.json" }
           }
       }
   }

   In this example, when an implementation encounters the <#/$defs/
   single> schema, it resolves the "$anchor" value as a fragment name
   against the current base URI to form <https://example.net/
   root.json#item>.

   When an implementation then looks inside the <#/items> schema, it
   encounters the <#item> reference, and resolves this to
   <https://example.net/root.json#item>, which it has seen defined in
   this same document and can therefore use automatically.

   When an implementation encounters the reference to "other.json", it
   resolves this to <https://example.net/other.json>, which is not
   defined in this document.  If a schema with that identifier has
   otherwise been supplied to the implementation, it can also be used
   automatically.

12.2.1.  Relative References

   Many hypermedia contexts (like HTML) make use of full URIs, anchors/
   names, and _relative references_ ([RFC3986], Section 5.1).  In JSON
   Schema, different contexts and use cases may make any of these three
   approaches the most convenient and least brittle; but relative
   references do require the most care in implementations.

   A fully conformant implementation MUST handle relative references,
   with the following guidance hopefully keeping implementation logic
   and overhead to a reasonable level.  A schema's $id acts as a base
   URI (see [RFC3986], Section 5.1.1) for relative references within the
   schema.







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   In accordance with [RFC3986], Section 5.1.2 regarding encapsulating
   entities, if an "$id" in a subschema is a relative reference, the
   base URI for resolving that reference is the URI of the parent schema
   resource.

   If no parent schema object explicitly identifies itself as a resource
   with "$id", the base URI is that of the entire document, as
   established by the steps given in Section 12.1.1.

12.2.2.  JSON Pointer fragments and embedded schema resources

   JSON Pointer URI fragments are constructed based on the structure of
   the schema document, allowing an embedded schema resource and its
   subschemas to be identified by JSON Pointer fragments relative to
   either its own canonical URI, or relative to any containing
   resource's URI.

   Conceptually, a set of linked schema resources should behave
   identically whether each resource is a separate document connected
   with schema references (Section 5.2.1), or is structured as a single
   document with one or more schema resources embedded as subschemas.

   Since URIs involving JSON Pointer fragments relative to the parent
   schema resource's URI cease to be valid when the embedded schema is
   moved to a separate document and referenced, applications and schemas
   SHOULD NOT use such URIs to identify embedded schema resources or
   locations within them.

   Consider the following schema document that contains another schema
   resource embedded within it:

   {
     "$id": "https://example.com/foo",
     "items": {
       "$id": "https://example.com/bar",
       "additionalProperties": { }
     }
   }

   The URI "https://example.com/foo#/items" points to the "items"
   schema, which is an embedded resource.  The canonical URI of that
   schema resource, however, is "https://example.com/bar".

   For the "additionalProperties" schema within that embedded resource,
   the URI "https://example.com/foo#/items/additionalProperties" points
   to the correct object, but that object's URI relative to its
   resource's canonical URI is "https://example.com/
   bar#/additionalProperties".



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   Now consider the following two schema resources linked by reference
   using a URI value for "$ref":

   {
     "$id": "https://example.com/foo",
     "items": {
       "$ref": "bar"
     }
   }

   {
     "$id": "https://example.com/bar",
     "additionalProperties": { }
   }

   Here we see that "https://example.com/bar#/additionalProperties",
   using a JSON Pointer fragment appended to the canonical URI of the
   "bar" schema resource, is still valid, while
   "https://example.com/foo#/items/additionalProperties", which relied
   on a JSON Pointer fragment appended to the canonical URI of the "foo"
   schema resource, no longer resolves to anything.

   Note also that "https://example.com/foo#/items" is valid in both
   arrangements, but resolves to a different value.  This URI ends up
   functioning similarly to a retrieval URI for a resource.  While this
   URI is valid, it is more robust to use the "$id" of the embedded or
   referenced resource unless it is specifically desired to identify the
   object containing the "$ref" in the second (non-embedded)
   arrangement.

   An implementation MAY choose not to support addressing schema
   resource contents by URIs using a base other than the resource's
   canonical URI, plus a JSON Pointer fragment relative to that base.
   Therefore, schema authors SHOULD NOT rely on such URIs, as using them
   may reduce interoperability.
   // This is to avoid requiring implementations to keep track of a
   // whole stack of possible base URIs and JSON Pointer fragments for
   // each, given that all but one will be fragile if the schema
   // resources are reorganized.  Some have argued that this is easy so
   // there is no point in forbidding it, while others have argued that
   // it complicates schema identification and should be forbidden.
   // Feedback on this topic is encouraged.  After some discussion, we
   // feel that we need to remove the use of "canonical" in favour of
   // talking about JSON Pointers which reference across schema resource
   // boundaries as undefined or even forbidden behavior
   // (https://github.com/json-schema-org/json-schema-spec/issues/937,
   // https://github.com/json-schema-org/json-schema-spec/issues/1183)




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   Further examples of such non-canonical URI construction, as well as
   the appropriate canonical URI-based fragments to use instead, are
   provided in Appendix A.

12.3.  Compound Documents

   A Compound Schema Document is defined as a JSON document (sometimes
   called a "bundled" schema) which has multiple embedded JSON Schema
   Resources bundled into the same document to ease transportation.

   Each embedded Schema Resource MUST be treated as an individual Schema
   Resource, following standard schema loading and processing
   requirements, including determining vocabulary support.

12.3.1.  Bundling

   The bundling process for creating a Compound Schema Document is
   defined as taking references (such as "$ref") to an external Schema
   Resource and embedding the referenced Schema Resources within the
   referring document.  Bundling SHOULD be done in such a way that all
   URIs (used for referencing) in the base document and any referenced/
   embedded documents do not require altering.

   Each embedded JSON Schema Resource MUST identify itself with a URI
   using the "$id" keyword, and SHOULD make use of the "$schema" keyword
   to identify the dialect it is using, in the root of the schema
   resource.  It is RECOMMENDED that the URI identifier value of "$id"
   be an absolute URI.

   When the Schema Resource referenced by a by-reference applicator is
   bundled, it is RECOMMENDED that the Schema Resource be located as a
   value of a "$defs" object at the containing schema's root.  The key
   of the "$defs" for the now embedded Schema Resource MAY be the "$id"
   of the bundled schema or some other form of application defined
   unique identifer (such as a UUID).  This key is not intended to be
   referenced in JSON Schema, but may be used by an application to aid
   the bundling process.

   A Schema Resource MAY be embedded in a location other than "$defs"
   where the location is defined as a schema value.

   A Bundled Schema Resource MUST NOT be bundled by replacing the schema
   object from which it was referenced, or by wrapping the Schema
   Resource in other applicator keywords.







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   In order to produce identical output, references in the containing
   schema document to the previously external Schema Resources MUST NOT
   be changed, and now resolve to a schema using the "$id" of an
   embedded Schema Resource.  Such identical output includes validation
   evaluation and URIs or paths used in resulting annotations or errors.

   While the bundling process will often be the main method for creating
   a Compound Schema Document, it is also possible and expected that
   some will be created by hand, potentially without individual Schema
   Resources existing on their own previously.

12.3.2.  Differing and Default Dialects

   When multiple schema resources are present in a single document,
   schema resources which do not define with which dialect they should
   be processed MUST be processed with the same dialect as the enclosing
   resource.

   Since any schema that can be referenced can also be embedded,
   embedded schema resources MAY specify different processing dialects
   using the "$schema" values from their enclosing resource.

12.3.3.  Validating

   Given that a Compound Schema Document may have embedded resources
   which identify as using different dialects, these documents SHOULD
   NOT be validated by applying a meta-schema to the Compound Schema
   Document as an instance.  It is RECOMMENDED that an alternate
   validation process be provided in order to validate Schema Documents.
   Each Schema Resource SHOULD be separately validated against its
   associated meta-schema.
   // If you know a schema is what's being validated, you can identify
   // if the schemas is a Compound Schema Document or not, by way of use
   // of "$id", which identifies an embedded resource when used not at
   // the document's root.

   A Compound Schema Document in which all embedded resources identify
   as using the same dialect, or in which "$schema" is omitted and
   therefore defaults to that of the enclosing resource, MAY be
   validated by applying the appropriate meta-schema.

12.4.  Caveats









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12.4.1.  Guarding Against Infinite Recursion

   A schema MUST NOT be run into an infinite loop evaluating input.  For
   example, if two schemas "#alice" and "#bob" both have an "allOf"
   property that refers to the other, a naive implementation might get
   stuck in an infinite recursive loop trying to validate the input.
   Schemas SHOULD NOT make use of infinite recursive nesting like this;
   the behavior is undefined.

12.4.2.  References to Possible Non-Schemas"

   Subschema objects (or booleans) are recognized by their use with
   known applicator keywords or with location-reserving keywords such as
   "$defs" (Section 5.2.2) that take one or more subschemas as a value.
   These keywords may be "$defs" and the standard applicators from this
   document, or extension keywords from a known vocabulary, or
   implementation-specific custom keywords.

   Multi-level structures of unknown keywords are capable of introducing
   nested subschemas, which would be subject to the processing rules for
   "$id".  Therefore, having a reference target in such an unrecognized
   structure cannot be reliably implemented, and the resulting behavior
   is undefined.  Similarly, a reference target under a known keyword,
   for which the value is known not to be a schema, results in undefined
   behavior in order to avoid burdening implementations with the need to
   detect such targets.
   // These scenarios are analogous to fetching a schema over HTTP but
   // receiving a response with a Content-Type other than application/
   // schema+json.  An implementation can certainly try to interpret it
   // as a schema, but the origin server offered no guarantee that it
   // actually is any such thing.  Therefore, interpreting it as such
   // has security implications and may produce unpredictable results.

   Note that single-level custom keywords with identical syntax and
   semantics to "$defs" do not allow for any intervening "$id" keywords,
   and therefore will behave correctly under implementations that
   attempt to use any reference target as a schema.  However, this
   behavior is

12.5.  RESTful / Hypermedia Schema References

   JSON and JSON schemas are not always used for HTTP resources or other
   hypermedia resources, and the rest of this document assumes no one
   protocol, nor does it even assume network access.  However since HTTP
   resources in JSON with JSON Schemas to describe them are pretty
   common in Web APIs, this section describes how to process JSON
   documents in a more RESTful manner when using protocols that support
   media types and Web linking ([RFC8288]).



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12.5.1.  Linking to a Schema

   It is RECOMMENDED that instances described by a schema provide a link
   to a downloadable JSON Schema using the link relation "describedby",
   as defined by Linked Data Protocol 1.0, ([LDP] Section 8.1.

   In HTTP, such links can be attached to any response using the Link
   header ([RFC8288]).  An example of such a header would be:

          Link: <https://example.com/my-hyper-schema>; rel="describedby"

12.5.2.  Usage Over HTTP

   When used for hypermedia systems over a network, HTTP ([RFC9110]) is
   frequently the protocol of choice for distributing schemas.
   Misbehaving clients can pose problems for server maintainers if they
   pull a schema over the network more frequently than necessary, when
   it's instead possible to cache a schema for a long period of time.

   HTTP servers SHOULD set long-lived caching headers on JSON Schemas.
   HTTP clients SHOULD observe caching headers and not re-request
   documents within their freshness period.  Distributed systems SHOULD
   make use of a shared cache and/or caching proxy.

   Clients SHOULD set or prepend a User-Agent header specific to the
   JSON Schema implementation or software product.  Since symbols are
   listed in decreasing order of significance, the JSON Schema library
   name/version should precede the more generic HTTP library name (if
   any).  For example:

        User-Agent: product-name/5.4.1 so-cool-json-schema/1.0.2 curl/7.43.0

   Clients SHOULD be able to make requests with a "From" header so that
   server operators can contact the owner of a potentially misbehaving
   script.

13.  Keyword Behaviors

   JSON Schema keywords fall into several general behavior categories.
   Assertions validate that an instance satisfies constraints, producing
   a boolean result.  Annotations attach information that applications
   may use in any way they see fit.  Applicators apply subschemas to
   parts of input and combine their results.








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   Extension keywords SHOULD stay within these categories, keeping in
   mind that annotations in particular are extremely flexible.  Complex
   behavior is usually better delegated to applications on the basis of
   annotation data than implemented directly as schema keywords.
   However, extension keywords MAY define other behaviors for
   specialized purposes.

   Evaluating an input against a schema involves processing all of the
   keywords in the schema against the appropriate locations within the
   input.  Typically, applicator keywords are processed until a schema
   object with no applicators (and therefore no subschemas) is reached.
   The appropriate location in the input is evaluated against the
   assertion and annotation keywords in the schema object.  The
   interactions of those keyword results to produce the schema object
   results are governed by Section 13.8.1.2, while the relationship of
   subschema results to the results of the applicator keyword that
   applied them is described by Section 13.6.

   Evaluation of a parent schema object can complete once all of its
   subschemas have been evaluated, although in some circumstances
   evaluation may be short-circuited due to assertion results.  When
   annotations are being collected, some assertion result short-
   circuiting is not possible due to the need to examine all subschemas
   for annotation collection, including those that cannot further change
   the assertion result.

13.1.  Lexical Scope and Dynamic Scope

   While most JSON Schema keywords can be evaluated on their own, or at
   most need to take into account the values or results of adjacent
   keywords in the same schema object, a few have more complex behavior.

   The lexical scope of a keyword is determined by the nested JSON data
   structure of objects and arrays.  The largest such scope is an entire
   schema document.  The smallest scope is a single schema object with
   no subschemas.

   Keywords MAY be defined with a partial value, such as a URI-
   reference, which must be resolved against another value, such as
   another URI-reference or a full URI, which is found through the
   lexical structure of the JSON document.  The "$id", "$ref", and
   "$dynamicRef" core keywords, and the "base" JSON Hyper-Schema
   keyword, are examples of this sort of behavior.

   Note that some keywords, such as "$schema", apply to the lexical
   scope of the entire schema resource, and therefore MUST only appear
   in a schema resource's root schema.




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   Other keywords may take into account the dynamic scope that exists
   during the evaluation of a schema, typically together with an input
   document.  The outermost dynamic scope is the schema object at which
   processing begins, even if it is not a schema resource root.  The
   path from this root schema to any particular keyword (that includes
   any "$ref" and "$dynamicRef" keywords that may have been resolved) is
   considered the keyword's "validation path."

   Lexical and dynamic scopes align until a reference keyword is
   encountered.  While following the reference keyword moves processing
   from one lexical scope into a different one, from the perspective of
   dynamic scope, following a reference is no different from descending
   into a subschema present as a value.  A keyword on the far side of
   that reference that resolves information through the dynamic scope
   will consider the originating side of the reference to be their
   dynamic parent, rather than examining the local lexically enclosing
   parent.

   The concept of dynamic scope is primarily used with "$dynamicRef" and
   "$dynamicAnchor", and should be considered an advanced feature and
   used with caution when defining additional keywords.  It also appears
   when reporting errors and collected annotations, as it may be
   possible to revisit the same lexical scope repeatedly with different
   dynamic scopes.  In such cases, it is important to inform the user of
   the dynamic path that produced the error or annotation.

13.2.  Keyword Interactions

   Keyword behavior MAY be defined in terms of the annotation results of
   subschemas (Section 4.1.2) and/or adjacent keywords (keywords within
   the same schema object) and their subschemas.  Such keywords MUST NOT
   result in a circular dependency.  Keywords MAY modify their behavior
   based on the presence or absence of another keyword in the same
   schema object (Section 4.1).

13.3.  Default Behaviors

   A missing keyword MUST NOT produce a false assertion result, MUST NOT
   produce annotation results, and MUST NOT cause any other schema to be
   evaluated as part of its own behavioral definition.  However, given
   that missing keywords do not contribute annotations, the lack of
   annotation results may indirectly change the behavior of other
   keywords.








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   In some cases, the missing keyword assertion behavior of a keyword is
   identical to that produced by a certain value, and keyword
   definitions SHOULD note such values where known.  However, even if
   the value which produces the default behavior would produce
   annotation results if present, the default behavior still MUST NOT
   result in annotations.

   Because annotation collection can add significant cost in terms of
   both computation and memory, implementations MAY opt out of this
   feature.  Keywords that are specified in terms of collected
   annotations SHOULD describe reasonable alternate approaches when
   appropriate.  This approach is demonstrated by the "items" and
   "additionalProperties" keywords in this document.

   Note that when no such alternate approach is possible for a keyword,
   implementations that do not support annotation collections will not
   be able to support those keywords or vocabularies that contain them.

13.4.  Handling unrecognized or unsupported keywords

   Implementations SHOULD treat keywords they do not recognize, or that
   they recognize but do not support, as annotations, where the value of
   the keyword is the value of the annotation.  Whether an
   implementation collects these annotations or not, they MUST otherwise
   ignore the keywords.

13.5.  Identifiers

   Identifiers define URIs for a schema, or affect how such URIs are
   resolved in schema references (Section 5.2.1), or both.  The Core
   vocabulary defined in this document defines several identifying
   keywords, most notably "$id".

   Canonical schema URIs MUST NOT change while processing an input, but
   keywords that affect URI-reference resolution MAY have behavior that
   is only fully determined at runtime.

   While custom identifier keywords are possible, vocabulary designers
   should take care not to disrupt the functioning of core keywords.
   For example, the "$dynamicAnchor" keyword in this specification
   limits its URI resolution effects to the matching "$dynamicRef"
   keyword, leaving the behavior of "$ref" undisturbed.









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13.6.  Applicators

   Applicators allow for building more complex schemas than can be
   accomplished with a single schema object.  Evaluation of an input
   against a schema document (Section 4.1) begins by applying the root
   schema (Section 4.1.2) to the complete input document.  From there,
   keywords known as applicators are used to determine which additional
   schemas are applied.  Such schemas may be applied in-place to the
   current location, or to a child location.

   The schemas to be applied may be present as subschemas comprising all
   or part of the keyword's value.  Alternatively, an applicator may
   refer to a schema elsewhere in the same schema document, or in a
   different one.  The mechanism for identifying such referenced schemas
   is defined by the keyword.

   Applicator keywords also define how subschema or referenced schema
   boolean assertion (Section 13.7) results are modified and/or combined
   to produce the boolean result of the applicator.  Applicators may
   apply any boolean logic operation to the assertion results of
   subschemas, but MUST NOT introduce new assertion conditions of their
   own.

   Annotation (Section 13.8) results from subschemas are preserved in
   accordance with Section 13.8.1 so that applications can decide how to
   interpret multiple values.  Applicator keywords do not play a direct
   role in this preservation.

   Annotation results are preserved along with the instance location and
   the location of the schema keyword, so that applications can decide
   how to interpret multiple values.

13.6.1.  Referenced and Referencing Schemas

   As noted in Section 13.6, an applicator keyword may refer to a schema
   to be applied, rather than including it as a subschema in the
   applicator's value.  In such situations, the schema being applied is
   known as the referenced schema, while the schema containing the
   applicator keyword is the referencing schema.

   While root schemas and subschemas are static concepts based on a
   schema's position within a schema document, referenced and
   referencing schemas are dynamic.  Different pairs of schemas may find
   themselves in various referenced and referencing arrangements during
   the evaluation of input against a schema.






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   For some by-reference applicators, such as "$ref" (Section 5.2.1),
   the referenced schema can be determined by static analysis of the
   schema document's lexical scope.  Others, such as "$dynamicRef" (with
   "$dynamicAnchor"), may make use of dynamic scoping, and therefore
   only be resolvable in the process of evaluating an input with the
   schema.

13.7.  Assertions

   JSON Schema can be used to assert constraints on a JSON document,
   which either passes or fails the assertions.  This approach can be
   used to validate conformance with the constraints, or document what
   is needed to satisfy them.

   JSON Schema implementations produce a single boolean result when
   evaluating an input against schema assertions.

   An input can only fail an assertion that is present in the schema.

13.7.1.  Assertions and Input Primitive Types

   Most assertions only constrain values within a certain primitive
   type.  When the type of the input is not of the type targeted by the
   keyword, the input is considered to conform to the assertion.

   For example, the "maxLength" keyword from the companion validation
   vocabulary ([I-D.bhutton-json-schema-validation]): will only restrict
   certain strings (that are too long) from being valid.  If the input
   is a number, boolean, null, array, or object, then it is valid
   against this assertion.

   This behavior allows keywords to be used more easily with inputs that
   can be of multiple primitive types.  The companion validation
   vocabulary also includes a "type" keyword which can independently
   restrict the input to one or more primitive types.  This allows for a
   concise expression of use cases such as a function that might return
   either a string of a certain length or a null value:

   {
       "type": ["string", "null"],
       "maxLength": 255
   }









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   If "maxLength" also restricted the input type to be a string, then
   this would be substantially more cumbersome to express because the
   example as written would not actually allow null values.  Each
   keyword is evaluated separately unless explicitly specified
   otherwise, so if "maxLength" restricted the input to strings, then
   including "null" in "type" would not have any useful effect.

13.8.  Annotations

   JSON Schema can annotate an instance with information, whenever the
   instance validates against the schema object containing the
   annotation, and all of its parent schema objects.  The information
   can be a simple value, or can be calculated based on the instance
   contents.

   Annotations are attached to specific locations in an instance.  Since
   many subschemas can be applied to any single location, applications
   may need to decide how to handle differing annotation values being
   attached to the same instance location by the same schema keyword in
   different schema objects.

   Unlike assertion results, annotation data can take a wide variety of
   forms, which are provided to applications to use as they see fit.
   JSON Schema implementations are not expected to make use of the
   collected information on behalf of applications.

   Unless otherwise specified, the value of an annotation keyword is the
   keyword's value.  However, other behaviors are possible.  For
   example, JSON Hyper-Schema's ([I-D.handrews-json-schema-hyperschema])
   "links" keyword is a complex annotation that produces a value based
   in part on the instance data.

   While "short-circuit" evaluation is possible for assertions,
   collecting annotations requires examining all schemas that apply to
   an instance location, even if they cannot change the overall
   assertion result.  The only exception is that subschemas of a schema
   object that has failed validation MAY be skipped, as annotations are
   not retained for failing schemas.

13.8.1.  Collecting Annotations

   Annotations are collected by keywords that explicitly define
   annotation-collecting behavior.  Note that boolean schemas cannot
   produce annotations as they do not make use of keywords.

   A collected annotation MUST include the following information:

   *  The name of the keyword that produces the annotation



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   *  The instance location to which it is attached, as a JSON Pointer

   *  The schema location path, indicating how reference keywords such
      as "$ref" were followed to reach the absolute schema location.

   *  The absolute schema location of the attaching keyword, as a URI.
      This MAY be omitted if it is the same as the schema location path
      from above.

   *  The attached value(s)

13.8.1.1.  Distinguishing Among Multiple Values

   Applications MAY make decisions on which of multiple annotation
   values to use based on the schema location that contributed the
   value.  This is intended to allow flexible usage.  Collecting the
   schema location facilitates such usage.

   For example, consider this schema, which uses annotations and
   assertions from the validation specification
   ([I-D.bhutton-json-schema-validation]):

   Note that some lines are wrapped for clarity.




























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   {
     "title": "Feature list",
     "type": "array",
     "prefixItems": [
       {
         "title": "Feature A",
         "properties": {
           "enabled": {
             "$ref": "#/$defs/enabledToggle",
             "default": true
           }
         }
       },
       {
         "title": "Feature B",
         "properties": {
           "enabled": {
             "description": "If set to null, Feature B inherits the enabled value from Feature A",
             "$ref": "#/$defs/enabledToggle"
           }
         }
       }
     ],
     "$defs": {
       "enabledToggle": {
         "title": "Enabled",
         "description": "Whether the feature is enabled (true), disabled (false), or under automatic control (null)",
         "type": ["boolean", "null"],
         "default": null
       }
     }
   }

   In this example, both Feature A and Feature B make use of the re-
   usable "enabledToggle" schema.  That schema uses the "title",
   "description", and "default" annotations.  Therefore the application
   has to decide how to handle the additional "default" value for
   Feature A, and the additional "description" value for Feature B.

   The application programmer and the schema author need to agree on the
   usage.  For this example, let's assume that they agree that the most
   specific "default" value will be used, and any additional, more
   generic "default" values will be silently ignored.  Let's also assume
   that they agree that all "description" text is to be used, starting
   with the most generic, and ending with the most specific.  This
   requires the schema author to write descriptions that work when
   combined in this way.




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   The application can use the schema location path to determine which
   values are which.  The values in the feature's immediate "enabled"
   property schema are more specific, while the values under the re-
   usable schema that is referenced to with "$ref" are more generic.
   The schema location path will show whether each value was found by
   crossing a "$ref" or not.

   Feature A will therefore use a default value of true, while Feature B
   will use the generic default value of null.  Feature A will only have
   the generic description from the "enabledToggle" schema, while
   Feature B will use that description, and also append its locally
   defined description that explains how to interpret a null value.

   Note that there are other reasonable approaches that a different
   application might take.  For example, an application may consider the
   presence of two different values for "default" to be an error,
   regardless of their schema locations.

13.8.1.2.  Annotations and Assertions

   Schema objects that produce a false assertion result MUST NOT produce
   any annotation results, whether from their own keywords or from
   keywords in subschemas.

   Note that the overall schema results may still include annotations
   collected from other schema locations.  Given this schema:

   {
       "oneOf": [
           {
               "title": "Integer Value",
               "type": "integer"
           },
           {
               "title": "String Value",
               "type": "string"
           }
       ]
   }

   Against the input "This is a string", the title annotation "Integer
   Value" is discarded because the type assertion in that schema object
   fails.  The title annotation "String Value" is kept, as the input
   passes the string type assertions.







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13.9.  Reserved Locations

   A fourth category of keywords simply reserve a location to hold re-
   usable components or data of interest to schema authors that is not
   suitable for re-use.  These keywords do not affect validation or
   annotation results.  Their purpose in the core vocabulary is to
   ensure that locations are available for certain purposes and will not
   be redefined by extension keywords.

   While these keywords do not directly affect results, as explained in
   Section 12.4.2 unrecognized extension keywords that reserve locations
   for re-usable schemas may have undesirable interactions with
   references in certain circumstances.

13.10.  Loading Input Data

   While none of the vocabularies defined as part of this or the
   associated documents define a keyword which may target and/or load
   input data, it is possible that other vocabularies may wish to do so.

   Keywords MAY be defined to use JSON Pointers or Relative JSON
   Pointers to examine parts of an input outside the current evaluation
   location.

   Keywords that allow adjusting the location using a Relative JSON
   Pointer SHOULD default to using the current location if a default is
   desireable.

14.  Output Formatting

   JSON Schema is defined to be platform-independent.  As such, to
   increase compatibility across platforms, implementations SHOULD
   conform to a standard validation output format.  This section
   describes the minimum requirements that consumers will need to
   properly interpret validation results.

14.1.  Format

   JSON Schema output is defined using the JSON Schema data model.
   Implementations MAY deviate from this as supported by their specific
   languages and platforms, however it is RECOMMENDED that the output be
   convertible to the JSON format defined herein via serialization or
   other means.

14.2.  Output Formats

   This specification defines four output formats.  See the "Output
   Structure" section for the requirements of each format.



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   *  Flag - A boolean which simply indicates the overall validation
      result with no further details.

   *  Basic - Provides validation information in a flat list structure.

   *  Detailed - Provides validation information in a condensed
      hierarchical structure based on the structure of the schema.

   *  Verbose - Provides validation information in an uncondensed
      hierarchical structure that matches the exact structure of the
      schema.

   An implementation SHOULD provide at least one of the "flag", "basic",
   or "detailed" format and MAY provide the "verbose" format.  If it
   provides one or more of the "detailed" or "verbose" formats, it MUST
   also provide the "flag" format.  Implementations SHOULD specify in
   their documentation which formats they support.

14.3.  Minimum Information

   Beyond the simplistic "flag" output, additional information is useful
   to aid in debugging a schema or input.  Each sub-result SHOULD
   contain the information contained within this section at a minimum.

   A single object that contains all of these components is considered
   an output unit.

   Implementations MAY elect to provide additional information.

14.3.1.  Keyword Relative Location

   The relative location of the validating keyword that follows the
   validation path.  The value MUST be expressed as a JSON Pointer, and
   it MUST include any by-reference applicators such as "$ref" or
   "$dynamicRef".

   /properties/width/$ref/minimum

   Note that this pointer may not be resolvable by the normal JSON
   Pointer process due to the inclusion of these by-reference applicator
   keywords.

   The JSON key for this information is "keywordLocation".








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14.3.2.  Keyword Absolute Location

   The absolute, dereferenced location of the validating keyword.  The
   value MUST be expressed as a full URI using the canonical URI of the
   relevant schema resource with a JSON Pointer fragment, and it MUST
   NOT include by-reference applicators such as "$ref" or "$dynamicRef"
   as non-terminal path components.  It MAY end in such keywords if the
   error or annotation is for that keyword, such as an unresolvable
   reference.
   // Note that "absolute" here is in the sense of "absolute filesystem
   // path" (meaning the complete location) rather than the "absolute-
   // URI" terminology from RFC 3986 (meaning with scheme but without
   // fragment).  Keyword absolute locations will have a fragment in
   // order to identify the keyword.

   https://example.com/schemas/common#/$defs/count/minimum

   This information MAY be omitted only if either the dynamic scope did
   not pass over a reference or if the schema does not declare an
   absolute URI as its "$id".

   The JSON key for this information is "absoluteKeywordLocation".

14.3.3.  Instance Location

   The location of the JSON value within the instance.  The value MUST
   be expressed as a JSON Pointer.

   The JSON key for this information is "instanceLocation".

14.3.4.  Error or Annotation

   The error or annotation that is produced by the validation.

   For errors, the specific wording for the message is not defined by
   this specification.  Implementations will need to provide this.

   For annotations, each keyword that produces an annotation specifies
   its format.  By default, it is the keyword's value.

   The JSON key for failed validations is "error"; for successful
   validations it is "annotation".

14.3.5.  Nested Results

   For the two hierarchical structures, this property will hold nested
   errors and annotations.




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   The JSON key for nested results in failed validations is "errors";
   for successful validations it is "annotations".  Note the plural
   forms, as a keyword with nested results can also have a local error
   or annotation.

14.4.  Output Structure

   The output MUST be an object containing a boolean property named
   "valid".  When additional information about the result is required,
   the output MUST also contain "errors" or "annotations" as described
   below.

   *  "valid" - a boolean value indicating the overall validation
      success or failure

   *  "errors" - the collection of errors or annotations produced by a
      failed validation

   *  "annotations" - the collection of errors or annotations produced
      by a successful validation

   For these examples, the following schema and input will be used.

   {
     "$id": "https://example.com/polygon",
     "$schema": "https://json-schema.org/draft/2020-12/schema",
     "$defs": {
       "point": {
         "type": "object",
         "properties": {
           "x": { "type": "number" },
           "y": { "type": "number" }
         },
         "additionalProperties": false,
         "required": [ "x", "y" ]
       }
     },
     "type": "array",
     "items": { "$ref": "#/$defs/point" },
     "minItems": 3
   }










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   [
     {
       "x": 2.5,
       "y": 1.3
     },
     {
       "x": 1,
       "z": 6.7
     }
   ]

   This input will fail validation and produce errors, but it's trivial
   to deduce examples for passing schemas that produce annotations.

   Specifically, the errors it will produce are:

   *  The second object is missing a "y" property.

   *  The second object has a disallowed "z" property.

   *  There are only two objects, but three are required.

   Note that the error message wording as depicted in these examples is
   not a requirement of this specification.  Implementations SHOULD
   craft error messages tailored for their audience or provide a
   templating mechanism that allows their users to craft their own
   messages.

14.4.1.  Flag

   In the simplest case, merely the boolean result for the "valid" valid
   property needs to be fulfilled.

   {
     "valid": false
   }

   Because no errors or annotations are returned with this format, it is
   RECOMMENDED that implementations use short-circuiting logic to return
   failure or success as soon as the outcome can be determined.  For
   example, if an "anyOf" keyword contains five sub-schemas, and the
   second one passes, there is no need to check the other three.  The
   logic can simply return with success.

14.4.2.  Basic

   The "Basic" structure is a flat list of output units.




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   {
     "valid": false,
     "errors": [
       {
         "keywordLocation": "",
         "instanceLocation": "",
         "error": "A subschema had errors."
       },
       {
         "keywordLocation": "/items/$ref",
         "absoluteKeywordLocation":
           "https://example.com/polygon#/$defs/point",
         "instanceLocation": "/1",
         "error": "A subschema had errors."
       },
       {
         "keywordLocation": "/items/$ref/required",
         "absoluteKeywordLocation":
           "https://example.com/polygon#/$defs/point/required",
         "instanceLocation": "/1",
         "error": "Required property 'y' not found."
       },
       {
         "keywordLocation": "/items/$ref/additionalProperties",
         "absoluteKeywordLocation":
           "https://example.com/polygon#/$defs/point/additionalProperties",
         "instanceLocation": "/1/z",
         "error": "Additional property 'z' found but was invalid."
       },
       {
         "keywordLocation": "/minItems",
         "instanceLocation": "",
         "error": "Expected at least 3 items but found 2"
       }
     ]
   }

14.4.3.  Detailed

   The "Detailed" structure is based on the schema and can be more
   readable for both humans and machines.  Having the structure
   organized this way makes associations between the errors more
   apparent.  For example, the fact that the missing "y" property and
   the extra "z" property both stem from the same location in the
   instance is not immediately obvious in the "Basic" structure.  In a
   hierarchy, the correlation is more easily identified.

   The following rules govern the construction of the results object:



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   *  All applicator keywords ("*Of", "$ref", "if"/"then"/"else", etc.)
      require a node.

   *  Nodes that have no children are removed.

   *  Nodes that have a single child are replaced by the child.

   Branch nodes do not require an error message or an annotation.

   {
     "valid": false,
     "keywordLocation": "",
     "instanceLocation": "",
     "errors": [
       {
         "valid": false,
         "keywordLocation": "/items/$ref",
         "absoluteKeywordLocation":
           "https://example.com/polygon#/$defs/point",
         "instanceLocation": "/1",
         "errors": [
           {
             "valid": false,
             "keywordLocation": "/items/$ref/required",
             "absoluteKeywordLocation":
               "https://example.com/polygon#/$defs/point/required",
             "instanceLocation": "/1",
             "error": "Required property 'y' not found."
           },
           {
             "valid": false,
             "keywordLocation": "/items/$ref/additionalProperties",
             "absoluteKeywordLocation":
               "https://example.com/polygon#/$defs/point/additionalProperties",
             "instanceLocation": "/1/z",
             "error": "Additional property 'z' found but was invalid."
           }
         ]
       },
       {
         "valid": false,
         "keywordLocation": "/minItems",
         "instanceLocation": "",
         "error": "Expected at least 3 items but found 2"
       }
     ]
   }




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14.4.4.  Verbose

   The "Verbose" structure is a fully realized hierarchy that exactly
   matches that of the schema.  This structure has applications in form
   generation and validation where the error's location is important.

   The primary difference between this and the "Detailed" structure is
   that all results are returned.  This includes sub-schema validation
   results that would otherwise be removed (e.g. annotations for failed
   validations, successful validations inside a not keyword, etc.).
   Because of this, it is RECOMMENDED that each node also carry a valid
   property to indicate the validation result for that node.

   Because this output structure can be quite large, a smaller example
   is given here for brevity.  The URI of the full output structure of
   the example above is: https://json-schema.org/draft/2020-12/output/
   verbose-example (https://json-schema.org/draft/2020-12/output/
   verbose-example).

   schema:

   {
     "$id": "https://example.com/polygon",
     "$schema": "https://json-schema.org/draft/2020-12/schema",
     "type": "object",
     "properties": {
       "validProp": true
     },
     "additionalProperties": false
   }

   input:

   {
     "validProp": 5,
     "disallowedProp": "value"
   }

   result:












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   {
     "valid": false,
     "keywordLocation": "",
     "instanceLocation": "",
     "errors": [
       {
         "valid": true,
         "keywordLocation": "/type",
         "instanceLocation": ""
       },
       {
         "valid": true,
         "keywordLocation": "/properties",
         "instanceLocation": ""
       },
       {
         "valid": false,
         "keywordLocation": "/additionalProperties",
         "instanceLocation": "",
         "errors": [
           {
             "valid": false,
             "keywordLocation": "/additionalProperties",
             "instanceLocation": "/disallowedProp",
             "error": "Additional property 'disallowedProp' found but was invalid."
           }
         ]
       }
     ]
   }

14.4.5.  Output validation schemas

   For convenience, JSON Schema has been provided to validate output
   generated by implementations.  Its URI is: https://json-schema.org/
   draft/2020-12/output/schema (https://json-schema.org/draft/2020-
   12/output/schema).

15.  Extensibility

15.1.  Non-JSON Inputs

   It is possible to use JSON Schema with a superset of the JSON Schema
   data model, where an input may be outside any of the six JSON data
   types.

   In this case, annotations still apply; but most validation keywords
   will not be useful, as they will always pass or always fail.



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   A custom vocabulary may define support for a superset of the core
   data model.  The schema itself may only be expressible in this
   superset; for example, to make use of the "const" keyword.

15.2.  Schema Vocabularies

   A schema vocabulary, or simply a vocabulary, is a set of keywords,
   their syntax, and their semantics.  A vocabulary is generally
   organized around a particular purpose.  Different uses of JSON
   Schema, such as validation, hypermedia, or user interface generation,
   will involve different sets of vocabularies.

   Vocabularies are the primary unit of re-use in JSON Schema, as schema
   authors can indicate what vocabularies are required or optional in
   order to process the schema.  Since vocabularies are identified by
   URIs in the meta-schema, generic implementations can load extensions
   to support previously unknown vocabularies.  While keywords can be
   supported outside of any vocabulary, there is no analogous mechanism
   to indicate individual keyword usage.

   A schema vocabulary can be defined by anything from an informal
   description to a standards proposal, depending on the audience and
   interoperability expectations.  In particular, in order to facilitate
   vocabulary use within non-public organizations, a vocabulary
   specification need not be published outside of its scope of use.

15.3.  Meta-Schemas

   A schema that itself describes a schema is called a meta-schema.
   Meta-schemas are used to validate JSON Schemas and specify which
   vocabularies they are using.

   Meta-schemas that use the "$vocabulary" keyword (Section 5.1.2) to
   declare the vocabularies in use MUST explicitly list the Core
   vocabulary, which MUST have a value of true indicating that it is
   required.

   Meta-schemas that do not use "$vocabulary" MUST be considered to
   require the Core vocabulary as if its URI were present with a value
   of true.

   Typically, a meta-schema will specify a set of vocabularies, and
   validate schemas that conform to the syntax of those vocabularies.
   However, meta-schemas and vocabularies are separate in order to allow
   meta-schemas to validate schema conformance more strictly or more
   loosely than the vocabularies' specifications call for.  Meta-schemas
   may also describe and validate additional keywords that are not part
   of a formal vocabulary.



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   Meta-schemas and vocabularies together are used to inform an
   implementation how to interpret a schema.  Every schema has a meta-
   schema, which can be declared using the "$schema" keyword.

   The meta-schema serves two purposes:

   1.  Declaring the vocabularies in use

       *  The "$vocabulary" keyword, when it appears in a meta-schema,
          declares which vocabularies are available to be used in
          schemas that refer to that meta-schema.  Vocabularies define
          keyword semantics, as well as their general syntax.

   2.  Describing valid schema syntax

       *  A schema MUST successfully validate against its meta-schema,
          which constrains the syntax of the available keywords.  The
          syntax described is expected to be compatible with the
          vocabularies declared; while it is possible to describe an
          incompatible syntax, such a meta-schema would be unlikely to
          be useful.

   Meta-schemas are separate from vocabularies to allow for vocabularies
   to be combined in different ways, and for meta-schema authors to
   impose additional constraints such as forbidding certain keywords, or
   performing unusually strict syntactical validation, as might be done
   during a development and testing cycle.  Each vocabulary typically
   identifies a meta-schema consisting only of the vocabulary's
   keywords.

   Meta-schema authoring is an advanced usage of JSON Schema, so the
   design of meta-schema features emphasizes flexibility over
   simplicity.

15.4.  Default JSON Schema Dialect

   The current URI for the default JSON Schema dialect meta-schema is
   https://json-schema.org/draft/2020-12/schema.  For schema author
   convenience, this meta-schema describes a dialect consisting of all
   vocabularies defined in this specification, as well as two former
   keywords which are reserved for a transitional period.  Individual
   vocabulary and vocabulary meta-schema URIs are given for each section
   below.  Certain vocabularies are optional to support, which is
   explained in detail in the relevant sections.

   Updated vocabulary and meta-schema URIs may be published between
   specification drafts in order to correct errors.




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16.  Security Considerations

   Both schemas and instances are JSON values.  As such, all security
   considerations defined in [RFC8259] apply.

   Instances and schemas are both frequently written by untrusted third
   parties, to be deployed on public Internet servers.  Implementations
   should take care that the parsing and validating against schemas does
   not consume excessive system resources.  Implementations MUST NOT
   fall into an infinite loop.

   A malicious party could cause an implementation to repeatedly collect
   a copy of a very large value as an annotation.  Implementations
   SHOULD guard against excessive consumption of system resources in
   such a scenario.

   Servers MUST ensure that malicious parties cannot change the
   functionality of existing schemas by uploading a schema with a pre-
   existing or very similar "$id".

   Individual JSON Schema vocabularies are liable to also have their own
   security considerations.  Consult the respective specifications for
   more information.

   Schema authors should take care with "$comment" contents, as a
   malicious implementation can display them to end-users in violation
   of a spec, or fail to strip them if such behavior is expected.

   A malicious schema author could place executable code or other
   dangerous material within a "$comment".  Implementations MUST NOT
   parse or otherwise take action based on "$comment" contents.

   JSON Schema validation allows the use of Regular Expressions, which
   have numerous different (often incompatible) implementations.  Some
   implementations allow the embedding of arbitrary code, which is
   outside the scope of JSON Schema and MUST NOT be permitted.  Regular
   expressions can often also be crafted to be extremely expensive to
   compute (with so-called "catastrophic backtracking"), resulting in a
   denial-of-service attack.

   Implementations that support validating or otherwise evaluating input
   string data based on "contentEncoding" and/or "contentMediaType" are
   at risk of evaluating data in an unsafe way based on misleading
   information.  Applications can mitigate this risk by only performing
   such processing when a relationship between the schema and input is
   established (e.g., they share the same authority).





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   Processing a media type or encoding is subject to the security
   considerations of that media type or encoding.  For example, the
   security considerations Scripting Media Types ([RFC4329]) apply when
   processing JavaScript or ECMAScript encoded within a JSON string.

17.  Interoperability Considerations

17.1.  Programming Language Independence

   JSON Schema is programming language agnostic, and supports the full
   range of values described in the data model.  Be aware, however, that
   some languages and JSON parsers may not be able to represent in
   memory the full range of values describable by JSON.

17.2.  Mathematical Integers

   Some programming languages and parsers use different internal
   representations for floating point numbers than they do for integers.

   For consistency, integer JSON numbers SHOULD NOT be encoded with a
   fractional part.

17.3.  Regular Expressions

   Keywords MAY use regular expressions to express constraints, or
   constrain the input value to be a regular expression.  These regular
   expressions SHOULD be valid according to the regular expression
   dialect described in [ECMA262], Section 21.2.1.

   Unless otherwise specified by a keyword, regular expressions MUST NOT
   be considered to be implicitly anchored at either end.  All regular
   expression keywords in this specification and its companion documents
   are un-anchored.

   Regular expressions SHOULD be built with the "u" flag (or equivalent)
   to provide Unicode support, or processed in such a way which provides
   Unicode support as defined by ECMA-262.

   Furthermore, given the high disparity in regular expression
   constructs support, schema authors SHOULD limit themselves to the
   following regular expression tokens:

   *  individual Unicode characters, as defined by the JSON
      specification ([RFC8259]);

   *  simple character classes ([abc]), range character classes ([a-z]);

   *  complemented character classes ([^abc], [^a-z]);



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   *  simple quantifiers: "+" (one or more), "*" (zero or more), "?"
      (zero or one), and their lazy versions ("+?", "*?", "??");

   *  range quantifiers: "{x}" (exactly x occurrences), "{x,y}" (at
      least x, at most y, occurrences), {x,} (x occurrences or more),
      and their lazy versions;

   *  the beginning-of-input ("^") and end-of-input ("$") anchors;

   *  simple grouping ("(...)") and alternation ("|").

   Finally, implementations MUST NOT take regular expressions to be
   anchored, neither at the beginning nor at the end.  This means, for
   instance, the pattern "es" matches "expression".

18.  IANA Considerations

18.1.  application/schema+json

   The proposed MIME media type for JSON Schema is defined as follows:

   *  Type name: application

   *  Subtype name: schema+json

   *  Required parameters: N/A

   *  Encoding considerations: Encoding considerations are identical to
      those specified for the "application/json" media type.  See JSON
      ([RFC8259]).

   *  Security considerations: See Section 16 above.

   *  Interoperability considerations: See Section 17.1, Section 17.2,
      and Section 17.3 above.

   *  Fragment identifier considerations: See Section 4.4.

18.2.  application/schema-instance+json

   The proposed MIME media type for JSON Schema Instances that require a
   JSON Schema-specific media type is defined as follows:

   *  Type name: application

   *  Subtype name: schema-instance+json

   *  Required parameters: N/A



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   *  Encoding considerations: Encoding considerations are identical to
      those specified for the "application/json" media type.  See JSON
      ([RFC8259]).

   *  Security considerations: See Section 16 above.

   *  Interoperability considerations: See Section 17.1, Section 17.2,
      and Section 17.3 above.

   *  Fragment identifier considerations: See Section 4.4.

19.  References

19.1.  Normative References

   [ECMA262]  European Computer Manufacturers Association, "ECMAScript
              Language Specification 5.1 Edition", ECMA Standard ECMA-
              262, June 2011, <http://www.ecma-
              international.org/publications/files/ecma-st/ECMA-
              262.pdf>.

   [I-D.hha-relative-json-pointer]
              Luff, G., Andrews, H., and B. Hutton, "Relative JSON
              Pointers", Work in Progress, Internet-Draft, draft-hha-
              relative-json-pointer-00, 19 June 2023,
              <https://datatracker.ietf.org/doc/html/draft-hha-relative-
              json-pointer-00>.

   [LDP]      Speicher, S., Arwe, J., and A. Malhotra, "Linked Data
              Platform 1.0", W3C Recommendation REC-ldp-20150226, 26
              February 2015,
              <http://www.w3.org/TR/2015/REC-ldp-20150226/>.

   [RFC1123]  Braden, R., Ed., "Requirements for Internet Hosts -
              Application and Support", STD 3, RFC 1123,
              DOI 10.17487/RFC1123, October 1989,
              <https://www.rfc-editor.org/rfc/rfc1123>.

   [RFC2045]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996,
              <https://www.rfc-editor.org/rfc/rfc2045>.

   [RFC2046]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part Two: Media Types", RFC 2046,
              DOI 10.17487/RFC2046, November 1996,
              <https://www.rfc-editor.org/rfc/rfc2046>.




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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/rfc/rfc2119>.

   [RFC2673]  Crawford, M., "Binary Labels in the Domain Name System",
              RFC 2673, DOI 10.17487/RFC2673, August 1999,
              <https://www.rfc-editor.org/rfc/rfc2673>.

   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
              <https://www.rfc-editor.org/rfc/rfc3339>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/rfc/rfc3986>.

   [RFC3987]  Duerst, M. and M. Suignard, "Internationalized Resource
              Identifiers (IRIs)", RFC 3987, DOI 10.17487/RFC3987,
              January 2005, <https://www.rfc-editor.org/rfc/rfc3987>.

   [RFC4122]  Leach, P., Mealling, M., and R. Salz, "A Universally
              Unique IDentifier (UUID) URN Namespace", RFC 4122,
              DOI 10.17487/RFC4122, July 2005,
              <https://www.rfc-editor.org/rfc/rfc4122>.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <https://www.rfc-editor.org/rfc/rfc4291>.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
              <https://www.rfc-editor.org/rfc/rfc4648>.

   [RFC5321]  Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
              DOI 10.17487/RFC5321, October 2008,
              <https://www.rfc-editor.org/rfc/rfc5321>.

   [RFC5890]  Klensin, J., "Internationalized Domain Names for
              Applications (IDNA): Definitions and Document Framework",
              RFC 5890, DOI 10.17487/RFC5890, August 2010,
              <https://www.rfc-editor.org/rfc/rfc5890>.

   [RFC5891]  Klensin, J., "Internationalized Domain Names in
              Applications (IDNA): Protocol", RFC 5891,
              DOI 10.17487/RFC5891, August 2010,
              <https://www.rfc-editor.org/rfc/rfc5891>.



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   [RFC6531]  Yao, J. and W. Mao, "SMTP Extension for Internationalized
              Email", RFC 6531, DOI 10.17487/RFC6531, February 2012,
              <https://www.rfc-editor.org/rfc/rfc6531>.

   [RFC6570]  Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
              and D. Orchard, "URI Template", RFC 6570,
              DOI 10.17487/RFC6570, March 2012,
              <https://www.rfc-editor.org/rfc/rfc6570>.

   [RFC6839]  Hansen, T. and A. Melnikov, "Additional Media Type
              Structured Syntax Suffixes", RFC 6839,
              DOI 10.17487/RFC6839, January 2013,
              <https://www.rfc-editor.org/rfc/rfc6839>.

   [RFC6901]  Bryan, P., Ed., Zyp, K., and M. Nottingham, Ed.,
              "JavaScript Object Notation (JSON) Pointer", RFC 6901,
              DOI 10.17487/RFC6901, April 2013,
              <https://www.rfc-editor.org/rfc/rfc6901>.

   [RFC8259]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/rfc/rfc8259>.

   [RFC8288]  Nottingham, M., "Web Linking", RFC 8288,
              DOI 10.17487/RFC8288, October 2017,
              <https://www.rfc-editor.org/rfc/rfc8288>.

   [XMLNS]    Bray, T., Hollander, D., Layman, A., Tobin, R., and H.
              Thompson, "Namespaces in XML 1.0 (Third Edition)", W3C
              Recommendation REC-xml-names-20091208, 8 December 2009,
              <http://www.w3.org/TR/2009/REC-xml-names-20091208/>.

19.2.  Informative References

   [I-D.bhutton-json-schema-validation]
              Wright, A., Andrews, H., and B. Hutton, "JSON Schema
              Validation: A Vocabulary for Structural Validation of
              JSON", Work in Progress, Internet-Draft, draft-bhutton-
              json-schema-validation-01, 10 June 2022,
              <https://datatracker.ietf.org/doc/html/draft-bhutton-json-
              schema-validation-01>.









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   [I-D.handrews-json-schema-hyperschema]
              Andrews, H. and A. Wright, "JSON Hyper-Schema: A
              Vocabulary for Hypermedia Annotation of JSON", Work in
              Progress, Internet-Draft, draft-handrews-json-schema-
              hyperschema-02, 17 September 2019,
              <https://datatracker.ietf.org/doc/html/draft-handrews-
              json-schema-hyperschema-02>.

   [RFC4329]  Hoehrmann, B., "Scripting Media Types", RFC 4329,
              DOI 10.17487/RFC4329, April 2006,
              <https://www.rfc-editor.org/rfc/rfc4329>.

   [RFC6596]  Ohye, M. and J. Kupke, "The Canonical Link Relation",
              RFC 6596, DOI 10.17487/RFC6596, April 2012,
              <https://www.rfc-editor.org/rfc/rfc6596>.

   [RFC9110]  Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
              Ed., "HTTP Semantics", STD 97, RFC 9110,
              DOI 10.17487/RFC9110, June 2022,
              <https://www.rfc-editor.org/rfc/rfc9110>.

   [W3C.WD-fragid-best-practices-20121025]
              Tennison, J., Ed., "Best Practices for Fragment
              Identifiers and Media Type Definitions", W3C WD WD-fragid-
              best-practices-20121025, W3C WD-fragid-best-practices-
              20121025, 25 October 2012, <https://www.w3.org/TR/2012/WD-
              fragid-best-practices-20121025/>.

Appendix A.  Schema identification examples

   Consider the following schema, which shows "$id" being used to
   identify both the root schema and various subschemas, and "$anchor"
   being used to define plain name fragment identifiers.


















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   {
       "$id": "https://example.com/root.json",
       "$defs": {
           "A": { "$anchor": "foo" },
           "B": {
               "$id": "other.json",
               "$defs": {
                   "X": { "$anchor": "bar" },
                   "Y": {
                       "$id": "t/inner.json",
                       "$anchor": "bar"
                   }
               }
           },
           "C": {
               "$id": "urn:uuid:ee564b8a-7a87-4125-8c96-e9f123d6766f"
           }
       }
   }

   The schemas at the following URI-encoded JSON Pointers ([RFC6901],
   relative to the root schema) have the following base URIs, and are
   identifiable by any listed URI in accordance with Section 4.4 and
   Section 12.2.2 above.

   *  # (document root)

      -  canonical (and base) URI: https://example.com/root.json

      -  canonical resource URI plus pointer fragment:
         https://example.com/root.json#

   *  #/$defs/A

      -  base URI: https://example.com/root.json

      -  canonical resource URI plus plain fragment:
         https://example.com/root.json#foo

      -  canonical resource URI plus pointer fragment:
         https://example.com/root.json#/$defs/A

   *  #/$defs/B

      -  canonical (and base) URI: https://example.com/other.json

      -  canonical resource URI plus pointer fragment:
         https://example.com/other.json#



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      -  base URI of enclosing (root.json) resource plus fragment:
         https://example.com/root.json#/$defs/B

   *  #/$defs/B/$defs/X

      -  base URI: https://example.com/other.json

      -  canonical resource URI plus plain fragment:
         https://example.com/other.json#bar

      -  canonical resource URI plus pointer fragment:
         https://example.com/other.json#/$defs/X

      -  base URI of enclosing (root.json) resource plus fragment:
         https://example.com/root.json#/$defs/B/$defs/X

   *  #/$defs/B/$defs/Y

      -  canonical (and base) URI: https://example.com/t/inner.json

      -  canonical URI plus plain fragment: https://example.com/t/
         inner.json#bar

      -  canonical URI plus pointer fragment: https://example.com/t/
         inner.json#

      -  base URI of enclosing (other.json) resource plus fragment:
         https://example.com/other.json#/$defs/Y

      -  base URI of enclosing (root.json) resource plus fragment:
         https://example.com/root.json#/$defs/B/$defs/Y

   *  #/$defs/C

      -  canonical (and base) URI: urn:uuid:ee564b8a-
         7a87-4125-8c96-e9f123d6766f

      -  canonical URI plus pointer fragment: urn:uuid:ee564b8a-
         7a87-4125-8c96-e9f123d6766f#

      -  base URI of enclosing (root.json) resource plus fragment:
         https://example.com/root.json#/$defs/C

   Note: The fragment part of the URI does not make it canonical or non-
   canonical, rather, the base URI used (as part of the full URI with
   any fragment) is what determines the canonical nature of the
   resulting full URI.
   // Multiple "canonical" URIs?  We Acknowledge this is potentially



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   // confusing, and direct you to read the CREF located in the JSON
   // Pointer fragments and embedded schema resources (Section 12.2.2)
   // section for futher comments.

Appendix B.  Manipulating schema documents and references

   Various tools have been created to rearrange schema documents based
   on how and where references ("$ref") appear.  This appendix discusses
   which use cases and actions are compliant with this specification.

B.1.  Bundling schema resources into a single document

   A set of schema resources intended for use together can be organized
   with each in its own schema document, all in the same schema
   document, or any granularity of document grouping in between.

   Numerous tools exist to perform various sorts of reference removal.
   A common case of this is producing a single file where all references
   can be resolved within that file.  This is typically done to simplify
   distribution, or to simplify coding so that various invocations of
   JSON Schema libraries do not have to keep track of and load a large
   number of resources.

   This transformation can be safely and reversibly done as long as all
   static references (e.g. "$ref") use URI-references that resolve to
   URIs using the canonical resource URI as the base, and all schema
   resources have an absolute-URI as the "$id" in their root schema.

   With these conditions met, each external resource can be copied under
   "$defs", without breaking any references among the resources' schema
   objects, and without changing any aspect of validation or annotation
   results.  The names of the schemas under "$defs" do not affect
   behavior, assuming they are each unique, as they do not appear in the
   canonical URIs for the embedded resources.

B.2.  Reference removal is not always safe

   Attempting to remove all references and produce a single schema
   document does not, in all cases, produce a schema with identical
   behavior to the original form.

   Since "$ref" is now treated like any other keyword, with other
   keywords allowed in the same schema objects, fully supporting non-
   recursive "$ref" removal in all cases can require relatively complex
   schema manipulations.  It is beyond the scope of this specification
   to determine or provide a set of safe "$ref" removal transformations,
   as they depend not only on the schema structure but also on the
   intended usage.



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Appendix C.  Example of recursive schema extension

   Consider the following two schemas describing a simple recursive tree
   structure, where each node in the tree can have a "data" field of any
   type.  The first schema allows and ignores other instance properties.
   The second is more strict and only allows the "data" and "children"
   properties.  An example input with "data" misspelled as "daat" is
   also shown.

   tree schema, extensible:

   {
       "$schema": "https://json-schema.org/draft/2020-12/schema",
       "$id": "https://example.com/tree",
       "$dynamicAnchor": "node",

       "type": "object",
       "properties": {
           "data": true,
           "children": {
               "type": "array",
               "items": {
                   "$dynamicRef": "#node"
               }
           }
       }
   }

   strict-tree schema, guards against misspelled properties:

   {
       "$schema": "https://json-schema.org/draft/2020-12/schema",
       "$id": "https://example.com/strict-tree",
       "$dynamicAnchor": "node",

       "$ref": "tree",
       "unevaluatedProperties": false
   }

   input with misspelled field:

   {
       "children": [ { "daat": 1 } ]
   }

   When we load these two schemas, we will notice the "$dynamicAnchor"
   named "node" (note the lack of "#" as this is just the name) present
   in each, resulting in the following full schema URIs:



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   *  "https://example.com/tree#node"

   *  "https://example.com/strict-tree#node"

   In addition, JSON Schema implementations keep track of the fact that
   these fragments were created with "$dynamicAnchor".

   If we apply the "strict-tree" schema to the input, we will follow the
   "$ref" to the "tree" schema, examine its "children" subschema, and
   find the "$dynamicRef": to "#node" (note the "#" for URI fragment
   syntax) in its "items" subschema.  That reference resolves to
   "https://example.com/tree#node", which is a URI with a fragment
   created by "$dynamicAnchor".  Therefore we must examine the dynamic
   scope before following the reference.

   At this point, the dynamic path is "#/$ref/properties/children/
   items/$dynamicRef", with a dynamic scope containing (from the
   outermost scope to the innermost):

   1.  "https://example.com/strict-tree#"

   2.  "https://example.com/tree#"

   3.  "https://example.com/tree#/properties/children"

   4.  "https://example.com/tree#/properties/children/items"

   Since we are looking for a plain name fragment, which can be defined
   anywhere within a schema resource, the JSON Pointer fragments are
   irrelevant to this check.  That means that we can remove those
   fragments and eliminate consecutive duplicates, producing:

   1.  "https://example.com/strict-tree"

   2.  "https://example.com/tree"

   In this case, the outermost resource also has a "node" fragment
   defined by "$dynamicAnchor".  Therefore instead of resolving the
   "$dynamicRef" to "https://example.com/tree#node", we resolve it to
   "https://example.com/strict-tree#node".

   This way, the recursion in the "tree" schema recurses to the root of
   "strict-tree", instead of only applying "strict-tree" to the input
   root, but applying "tree" to input children.

   This example shows both "$dynamicAnchor"s in the same place in each
   schema, specifically the resource root schema.  Since plain-name
   fragments are independent of the JSON structure, this would work just



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   as well if one or both of the node schema objects were moved under
   "$defs".  It is the matching "$dynamicAnchor" values which tell us
   how to resolve the dynamic reference, not any sort of correlation in
   JSON structure.

Appendix D.  Working with vocabularies

D.1.  Best practices for vocabulary and meta-schema authors"

   Vocabulary authors should take care to avoid keyword name collisions
   if the vocabulary is intended for broad use, and potentially combined
   with other vocabularies.  JSON Schema does not provide any formal
   namespacing system, but also does not constrain keyword names,
   allowing for any number of namespacing approaches.

   Vocabularies may build on each other, such as by defining the
   behavior of their keywords with respect to the behavior of keywords
   from another vocabulary, or by using a keyword from another
   vocabulary with a restricted or expanded set of acceptable values.
   Not all such vocabulary re-use will result in a new vocabulary that
   is compatible with the vocabulary on which it is built.  Vocabulary
   authors should clearly document what level of compatibility, if any,
   is expected.

   Meta-schema authors should not use "$vocabulary" to combine multiple
   vocabularies that define conflicting syntax or semantics for the same
   keyword.  As semantic conflicts are not generally detectable through
   schema validation, implementations are not expected to detect such
   conflicts.  If conflicting vocabularies are declared, the resulting
   behavior is undefined.

   Vocabulary authors SHOULD provide a meta-schema that validates the
   expected usage of the vocabulary's keywords on their own.  Such meta-
   schemas SHOULD not forbid additional keywords, and MUST not forbid
   any keywords from the Core vocabulary.

   It is recommended that meta-schema authors reference each
   vocabulary's meta-schema using the "allOf" (Section 6.2.1) keyword,
   although other mechanisms for constructing the meta-schema may be
   appropriate for certain use cases.

   The recursive nature of meta-schemas makes the "$dynamicAnchor" and
   "$dynamicRef" keywords particularly useful for extending existing
   meta-schemas, as can be seen in the JSON Hyper-Schema
   ([I-D.handrews-json-schema-hyperschema]) meta-schema which extends
   the Validation meta-schema.





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   Meta-schemas may impose additional constraints, including describing
   keywords not present in any vocabulary, beyond what the meta-schemas
   associated with the declared vocabularies describe.  This allows for
   restricting usage to a subset of a vocabulary, and for validating
   locally defined keywords not intended for re-use.

   However, meta-schemas should not contradict any vocabularies that
   they declare, such as by requiring a different JSON type than the
   vocabulary expects.  The resulting behavior is undefined.

   Meta-schemas intended for local use, with no need to test for
   vocabulary support in arbitrary implementations, can safely omit
   "$vocabulary" entirely.

D.2.  Example meta-schema with vocabulary declarations

   This meta-schema explicitly declares both the Core and Applicator
   vocabularies, together with an extension vocabulary, and combines
   their meta-schemas with an "allOf".  The extension vocabulary's meta-
   schema, which describes only the keywords in that vocabulary, is
   shown after the main example meta-schema.

   The main example meta-schema also restricts the usage of the
   Unevaluated vocabulary by forbidding the keywords prefixed with
   "unevaluated", which are particularly complex to implement.  This
   does not change the semantics or set of keywords defined by the other
   vocabularies.  It just ensures that schemas using this meta-schema
   that attempt to use the keywords prefixed with "unevaluated" will
   fail validation against this meta-schema.

   Finally, this meta-schema describes the syntax of a keyword,
   "localKeyword", that is not part of any vocabulary.  Presumably, the
   implementors and users of this meta-schema will understand the
   semantics of "localKeyword".  JSON Schema does not define any
   mechanism for expressing keyword semantics outside of vocabularies,
   making them unsuitable for use except in a specific environment in
   which they are understood.

   This meta-schema combines several vocabularies for general use.












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   {
     "$schema": "https://json-schema.org/draft/2020-12/schema",
     "$id": "https://example.com/meta/general-use-example",
     "$dynamicAnchor": "meta",
     "$vocabulary": {
       "https://json-schema.org/draft/2020-12/vocab/core": true,
       "https://json-schema.org/draft/2020-12/vocab/applicator": true,
       "https://json-schema.org/draft/2020-12/vocab/validation": true,
       "https://example.com/vocab/example-vocab": true
     },
     "allOf": [
       {"$ref": "https://json-schema.org/draft/2020-12/meta/core"},
       {"$ref": "https://json-schema.org/draft/2020-12/meta/applicator"},
       {"$ref": "https://json-schema.org/draft/2020-12/meta/validation"},
       {"$ref": "https://example.com/meta/example-vocab"}
     ],
     "patternProperties": {
       "^unevaluated": false
     },
     "properties": {
       "localKeyword": {
         "$comment": "Not in vocabulary, but validated if used",
         "type": "string"
       }
     }
   }

   This meta-schema describes only a single extension vocabulary.

   {
     "$schema": "https://json-schema.org/draft/2020-12/schema",
     "$id": "https://example.com/meta/example-vocab",
     "$dynamicAnchor": "meta",
     "$vocabulary": {
       "https://example.com/vocab/example-vocab": true
     },
     "type": ["object", "boolean"],
     "properties": {
       "minDate": {
         "type": "string",
         "pattern": "\d\d\d\d-\d\d-\d\d",
         "format": "date"
       }
     }
   }






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   As shown above, even though each of the single-vocabulary meta-
   schemas referenced in the general-use meta-schema's "allOf" declares
   its corresponding vocabulary, this new meta-schema must re-declare
   them.

   The standard meta-schemas that combine all vocabularies defined by
   the Core and Validation specification, and that combine all
   vocabularies defined by those specifications as well as the Hyper-
   Schema specification ([I-D.handrews-json-schema-hyperschema]),
   demonstrate additional complex combinations.  These URIs for these
   meta-schemas may be found in the Validation and Hyper-Schema
   specifications, respectively.

   While the general-use meta-schema can validate the syntax of
   "minDate", it is the vocabulary that defines the logic behind the
   semantic meaning of "minDate".  Without an understanding of the
   semantics (in this example, that the input value must be a date equal
   to or after the date provided as the keyword's value in the schema),
   an implementation can only validate the syntactic usage.  In this
   case, that means validating that it is a date-formatted string (using
   "pattern" to ensure that it is validated even when "format" functions
   purely as an annotation, as explained in the the validation
   specification ([I-D.bhutton-json-schema-validation]).

Appendix E.  References and generative use cases

   While the presence of references is expected to be transparent to
   validation results, generative use cases such as code generators and
   UI renderers often consider references to be semantically
   significant.

   To make such use case-specific semantics explicit, the best practice
   is to create an annotation keyword for use in the same schema object
   alongside of a reference keyword such as "$ref".

   For example, here is a hypothetical keyword for determining whether a
   code generator should consider the reference target to be a distinct
   class, and how those classes are related.  Note that this example is
   solely for illustrative purposes, and is not intended to propose a
   functional code generation keyword.











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   {
     "allOf": [
       {
         "classRelation": "is-a",
         "$ref": "classes/base.json"
       },
       {
         "$ref": "fields/common.json"
       }
     ],
     "properties": {
       "foo": {
         "classRelation": "has-a",
         "$ref": "classes/foo.json"
       },
       "date": {
         "$ref": "types/dateStruct.json"
       }
     }
   }

   Here, this schema represents some sort of object-oriented class.  The
   first reference in the "allOf" is noted as the base class.  The
   second is not assigned a class relationship, meaning that the code
   generator should combine the target's definition with this one as if
   no reference were involved.

   Looking at the properties, "foo" is flagged as object composition,
   while the "date" property is not.  It is simply a field with sub-
   fields, rather than an instance of a distinct class.

   This style of usage requires the annotation to be in the same object
   as the reference, which must be recognizable as a reference.

Appendix F.  Acknowledgments

   This draft is based on great amounts of superb work by creators and
   contributors to JSON Schema.  The authors of the 2020-12 spec include
   Ben Hutton and Greg Dennis.  Thanks also to Jason Desrosiers.

   Past contributors include, with thanks: Gary Court, Francis Galiegue,
   Kris Zyp, Geraint Luff Daniel Perrett, Erik Wilde, Evgeny Poberezkin,
   Brad Bowman, Gowry Sankar, Donald Pipowitch, Dave Finlay, Denis
   Laxalde, Phil Sturgeon, Shawn Silverman, and Karen Etheridge.







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Appendix G.  Change Log


   // This section to be removed before leaving Internet-Draft status.

G.1.  draft-dusseault-json-schema-00

   Compared to the "2020-12" version of JSON Schema, this draft makes
   the following changes.

   *  Consolidate the 2020-12 core and validation documents

   *  Delevel headers for a more readable Table of Contents

   *  Shift terminology to a terminology section

   *  Reorder conceptually: intro, keywords, processing and output,
      extensibility.

   *  Define input and instance as different things.

Authors' Addresses

   Lisa Dusseault
   Data Transfer Initiative
   Email: lisa@rtfm.com


   Austin Wright
   Email: aaa@bzfx.net


   Henry H. Andrews
   Email: andrews_henry@yahoo.com

















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