





Internet Architecture Board (IAB)                            H. Flanagan
Request for Comments: 7993                                    RFC Editor
Category: Informational                                    December 2016
ISSN: 2070-1721


           Cascading Style Sheets (CSS) Requirements for RFCs

Abstract

   The HTML format for RFCs assigns style guidance to a Cascading Style
   Sheet (CSS) specifically defined for the RFC Series.  The embedded,
   default CSS as included by the RFC Editor is expected to take into
   account accessibility needs and to be built along a responsive design
   model.  This document describes the requirements for the default CSS
   used by the RFC Editor.  The class names are based on the classes
   defined in "HTML for RFCs" (RFC 7992).

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Architecture Board (IAB)
   and represents information that the IAB has deemed valuable to
   provide for permanent record.  It represents the consensus of the
   Internet Architecture Board (IAB).  Documents approved for
   publication by the IAB are not a candidate for any level of Internet
   Standard; see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7993.

Copyright Notice

   Copyright (c) 2016 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
   (http://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.






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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Design Goal . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  General Requirements  . . . . . . . . . . . . . . . . . . . .   3
   4.  Page Layout . . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Title Page Header . . . . . . . . . . . . . . . . . . . .   4
     4.2.  Body  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.3.  Font Choices  . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Printing  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   7.  CSS Classes and Attributes  . . . . . . . . . . . . . . . . .   5
     7.1.  .alignCenter  . . . . . . . . . . . . . . . . . . . . . .   5
     7.2.  .alignRight . . . . . . . . . . . . . . . . . . . . . . .   5
     7.3.  .artwork  . . . . . . . . . . . . . . . . . . . . . . . .   5
       7.3.1.  .art-ascii-art  . . . . . . . . . . . . . . . . . . .   5
       7.3.2.  .art-logo . . . . . . . . . . . . . . . . . . . . . .   5
     7.4.  .cref . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     7.5.  .crefAnchor . . . . . . . . . . . . . . . . . . . . . . .   6
     7.6.  .crefSource . . . . . . . . . . . . . . . . . . . . . . .   6
     7.7.  .dlCompact  . . . . . . . . . . . . . . . . . . . . . . .   6
     7.8.  .dlHanging  . . . . . . . . . . . . . . . . . . . . . . .   6
     7.9.  .dlParallel . . . . . . . . . . . . . . . . . . . . . . .   6
     7.10. .docInfo  . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.11. .eref . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.12. .finalized  . . . . . . . . . . . . . . . . . . . . . . .   6
     7.13. .note . . . . . . . . . . . . . . . . . . . . . . . . . .   6
       7.13.1.  .rfcEditorRemove . . . . . . . . . . . . . . . . . .   6
     7.14. .olCompact  . . . . . . . . . . . . . . . . . . . . . . .   7
     7.15. .olPercent  . . . . . . . . . . . . . . . . . . . . . . .   7
     7.16. .pilcrow  . . . . . . . . . . . . . . . . . . . . . . . .   7
     7.17. .relref . . . . . . . . . . . . . . . . . . . . . . . . .   7
     7.18. .rendered . . . . . . . . . . . . . . . . . . . . . . . .   7
     7.19. .sourcecode . . . . . . . . . . . . . . . . . . . . . . .   7
     7.20. .toc  . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     7.21. .type . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     7.22. .ulCompact  . . . . . . . . . . . . . . . . . . . . . . .   8
     7.23. .ulEmpty  . . . . . . . . . . . . . . . . . . . . . . . .   8
     7.24. .url  . . . . . . . . . . . . . . . . . . . . . . . . . .   8
     7.25. .xref . . . . . . . . . . . . . . . . . . . . . . . . . .   8
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Appendix A.  List of Classes  . . . . . . . . . . . . . . . . . .  10
   IAB Members at the Time of Approval . . . . . . . . . . . . . . .  14
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  14
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  14



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1.  Introduction

   The HTML format for RFCs, described in [RFC7992], assigns style
   guidance to a Cascading Style Sheet (CSS) specifically defined for
   the RFC Series.  This CSS will be embedded in the published HTML, and
   it may be overridden by a locally defined CSS, as desired.  The
   embedded, default CSS as included by the RFC Editor is expected to
   take into account accessibility needs and to be built along a
   responsive design model.

   This document describes the requirements for the default CSS used by
   the RFC Editor.  Unless called out otherwise, any styling provided
   for these classes must not alter the natural language content in any
   visible way.  Many of these classes are provided to mark the elements
   semantically: elements using them should simply inherit their
   surrounding styling.  Exceptions are listed below.  A class is
   identified for Internet-Drafts, such that certain features found only
   in I-Ds may be made distinct in some fashion within those drafts.
   The requirements will only be applied to HTML documents published by
   the RFC Editor as per [RFC7990].

   The details included in this document are expected to change based on
   experience gained in implementing the new publication toolsets.
   Revised documents will be published capturing those changes as the
   toolsets are completed.  Other implementers must not expect those
   changes to remain backwards compatible with the details included in
   this document.

2.  Design Goal

   RFCs must be adaptable to a wide variety of devices and displays,
   accessible to assisted readers, and printable.

3.  General Requirements

   o  Support the display of the semantic HTML described in [RFC7992].

   o  Follow best practice for accessibility, as defined by the W3C's
      "Best Practices for Authoring HTML" [HTMLBP].

   o  Follow best practice for mobile devices, as defined by the W3C's
      "Best Practices for Authoring HTML".

   o  Allow for a broad range of internationalized scripts.







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4.  Page Layout

4.1.  Title Page Header

   The document header must be at the top of the document and include
   all information described in "RFC Style Guide" [RFC7322] and "RFC
   Streams, Headers, and Boilerplates" [RFC7841].

4.2.  Body

   The body of the document must conform to the following:

   o  Examples and code blocks must be in a fixed-width font

   o  ASCII art must be in a fixed-width font

   o  Reflow the text as the screen gets smaller and limit max width

   o  Block quotes must be indented

   o  Tables must allow for distinct header rows

   o  Paragraphs should include a hover-over paragraph identifier

   All anchor tags and URLs should be clearly distinguished as links,
   for example, through the use of color and/or text decoration,
   following appropriate accessibility standards.

4.3.  Font Choices

   o  Default to a sans-serif font family with broad Unicode support for
      web browser viewing.

   o  Default to a serif font family with broad Unicode support for
      printing.

   o  A fixed-width font must be used for code and artwork-tagged
      sections.

   o  All fonts should be publicly licensed and supported by all major
      web browsers.

5.  Printing

   The CSS must include support for a printer-friendly output.  The
   print rules should be a part of the embedded style sheet; consumers
   of an RFC may develop their own print-specific style sheet, as
   desired.



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6.  Lists

   Lists should provide ample whitespace between list elements for
   legibility unless a 'compact' class is specified (e.g., .dlCompact,
   .ulCompact, .olCompact).

7.  CSS Classes and Attributes

   This section describes the CSS classes that result in specific
   changes to the natural language content of a document.  A full list
   of available classes, not including basic selectors, is included in
   Appendix A.

7.1.  .alignCenter

   To be used with '.artwork' to indicate the figure should align in the
   center of the page flow.

7.2.  .alignRight

   To be used with '.artwork' to indicate the figure should align on the
   right of the page flow.

7.3.  .artwork

   These classes will mostly be styled as part of '.artwork'.  Specific
   classes may include '.art-ascii-art' and '.art-svg'.  Artwork will be
   held in its own block of space, centered in the page flow, and will
   not float.  Images should have a max width of 100% so views will
   scale properly across a variety of screens and devices.

7.3.1.  .art-ascii-art

   Must use a mono-spaced font.

7.3.2.  .art-logo

   No visible changes to the natural language content; keep in default
   style.  Note that such images are not currently allowed in RFCs.

7.4.  .cref

   A comment within an I-D; should be visually distinct.

   For I-Ds only; not for RFCs.






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7.5.  .crefAnchor

   A comment within an I-D; should be visually distinct.

   For I-Ds only; not for RFCs.

7.6.  .crefSource

   A comment within an I-D; should be visually distinct.

   For I-Ds only; not for RFCs.

7.7.  .dlCompact

   Use less spacing on a definition list than the default.

7.8.  .dlHanging

   Use the standard hanging indent for a definition list; indent terms.

7.9.  .dlParallel

   Do not use the standard hanging indent for a definition list; align
   terms and definitions along left side.

7.10.  .docInfo

   Hide from visible content.

7.11.  .eref

   Standard link formatting (underlined, change in color).

7.12.  .finalized

   Hide from visible content.

7.13.  .note

   Notes should be emphasized and distinct from normal paragraph text.

7.13.1.  .rfcEditorRemove

   An RFC Editor note may be added after the standard boilerplate.  It
   should be visually distinct to highlight final removal of the note by
   the RFC Editor.





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7.14.  .olCompact

   Use less spacing on a numbered list than the default.

7.15.  .olPercent

   If the style attribute from the source XML contains a percent sign, a
   particular style setting will be required to make this setting behave
   like an HTML ordered list.

7.16.  .pilcrow

   Pilcrows, when used as described in RFC 7992, should appear at the
   end of the paragraph, artwork, or sourcecode segment.  They should
   not appear until moused-over.  They should not show when printed, and
   they should not be selected when copied with a copy/paste function.

7.17.  .relref

   Should be clearly distinguished as links.

7.18.  .rendered

   Hide from visible content.

7.19.  .sourcecode

   Code examples or components should be in a fixed-width font if the
   human language used has an available fixed-width font option, and
   they should be visually distinct.  If no fixed-width font is
   available, use the default font for that human language.

7.20.  .toc

   The table of contents should be clearly distinguished using an
   indented, ordered list with the list style set to 'none', allowing
   for hyperlinked, in-line dotted number notation (e.g., 1., 1.1.,
   1.1.1.).

7.21.  .type

   No visible changes to the natural language content; keep in default
   style.








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7.22.  .ulCompact

   Use less spacing on a bulleted list than the default.

7.23.  .ulEmpty

   Indent from the margin of the previous paragraph.

7.24.  .url

   Should be clearly distinguished as links.

7.25.  .xref

   Should be clearly distinguished as links.

8.  Security Considerations

   Security vulnerabilities can be introduced through the CSS, as with
   CSS injection attacks [CSSATTACK].  In order to avoid or mitigate any
   attack vectors here, the CSS used must comply with the current CSS
   Specifications from the W3C.

9.  References

9.1.  Normative References

   [HTMLBP]   W3C, "Best Practices for Authoring HTML Current Status",
              <http://www.w3.org/standards/techs/htmlbp>.

   [RFC7841]  Halpern, J., Ed., Daigle, L., Ed., and O. Kolkman, Ed.,
              "RFC Streams, Headers, and Boilerplates", RFC 7841, DOI
              10.17487/RFC7841, May 2016,
              <http://www.rfc-editor.org/info/rfc7841>.

   [RFC7322]  Flanagan, H. and S. Ginoza, "RFC Style Guide", RFC 7322,
              DOI 10.17487/RFC7322, September 2014,
              <http://www.rfc-editor.org/info/rfc7322>.

   [RFC7990]  Flanagan, H., "RFC Format Framework", RFC 7990,
              DOI 10.17487/RFC7990, December 2016,
              <http://www.rfc-editor.org/info/rfc7990>.

   [RFC7992]  Hildebrand, J., Ed. and P. Hoffman, "HTML Format for
              RFCs", RFC 7992, DOI 10.17487/RFC7992, December 2016,
              <http://www.rfc-editor.org/info/rfc7992>.





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9.2.  Informative References

   [CSSATTACK]
              Huang, L-S., Weinberg, Z., Evans, C., and C. Jackson,
              "Protecting browsers from cross-origin CSS attacks", In
              Proceedings of the 17th ACM conference on Computer and
              communications security (CCS '10), pp. 619-629, 2010,
              <https://doi.org/10.1145/1866307.1866376>.











































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Appendix A.  List of Classes

   This section lists all the CSS classes.  Except for those also listed
   in Section 7, none of these result in specific changes to the natural
   language content of a document.

   o  .adr

   o  .alignCenter

   o  .alignRight

   o  .annotation

   o  .artwork

         .art-ascii-art

         .art-logo

         .art-svg

   o  .ascii

   o  .author

   o  .authors

   o  .bcp14

   o  .center

   o  .city

   o  .compact

   o  .country-name

   o  .cref












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   o  .crefAnchor

   o  .crefSource

   o  .dlCompact

   o  .dlHanging

   o  .dlParallel

   o  .docInfo

   o  .ears

   o  .email

   o  .eref

   o  .finalized

   o  .fn

   o  .index

   o  .indexChar

   o  .indexIndex

   o  .indexItem

   o  .indexPrimary

   o  .indexSubItem

   o  .initial

   o  .iref

   o  .irefItem

   o  .irefRefs

   o  .irefSubItem

   o  .label

   o  .left




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   o  .locality

   o  .nameRole

   o  .note

         .rfcEditorRemove

   o  .olCompact

   o  .olPercent

   o  .org

   o  .organization

   o  .pilcrow

   o  .postal-code

   o  .published

   o  .refContent

   o  .refDate

   o  .refInstance

   o  .refTitle

   o  .reference

   o  .region

   o  .relref

   o  .rendered

   o  .RFC

   o  .rfcEditorRemove

   o  .right

   o  .role

   o  .selfRef




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   o  .series

   o  .seriesInfo

   o  .sourcecode

         .lang-*

   o  .street-address

   o  .status

   o  .street-address

   o  .surname

   o  .tel

   o  .toc

   o  .type

   o  .ulCompact

   o  .ulEmpty

   o  .url

   o  .workgroup

   o  .xref

   o  .vcard


















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IAB Members at the Time of Approval

   The IAB members at the time this memo was approved were (in
   alphabetical order):

      Jari Arkko
      Ralph Droms
      Ted Hardie
      Joe Hildebrand
      Russ Housley
      Lee Howard
      Erik Nordmark
      Robert Sparks
      Andrew Sullivan
      Dave Thaler
      Martin Thomson
      Brian Trammell
      Suzanne Woolf

Acknowledgements

   With many thanks to the RFC Format Design Team for their efforts in
   making this transition successful: Nevil Brownlee (ISE), Tony Hansen,
   Joe Hildebrand, Paul Hoffman, Ted Lemon, Julian Reschke, Adam Roach,
   Alice Russo, Robert Sparks (Tools Team liaison), and Dave Thaler.

   Additional thanks to Arlen Johnson of Spherical Cow Group, LLC, for
   his assistance in clarifying the requirements in more CSS-designer-
   friendly language.

Author's Address

   Heather Flanagan
   RFC Editor

   Email: rse@rfc-editor.org
   URI:   http://orcid.org/0000-0002-2647-2220














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