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rfc:rfc7993

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.

Flanagan Informational [Page 1] RFC 7993 CSS Reqs for RFCs December 2016

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

Flanagan Informational [Page 2] RFC 7993 CSS Reqs for RFCs December 2016

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.

Flanagan Informational [Page 3] RFC 7993 CSS Reqs for RFCs December 2016

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.

Flanagan Informational [Page 4] RFC 7993 CSS Reqs for RFCs December 2016

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.

Flanagan Informational [Page 5] RFC 7993 CSS Reqs for RFCs December 2016

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.

Flanagan Informational [Page 6] RFC 7993 CSS Reqs for RFCs December 2016

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.

Flanagan Informational [Page 7] RFC 7993 CSS Reqs for RFCs December 2016

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>.

Flanagan Informational [Page 8] RFC 7993 CSS Reqs for RFCs December 2016

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>.

Flanagan Informational [Page 9] RFC 7993 CSS Reqs for RFCs December 2016

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

Flanagan Informational [Page 10] RFC 7993 CSS Reqs for RFCs December 2016

 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

Flanagan Informational [Page 11] RFC 7993 CSS Reqs for RFCs December 2016

 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

Flanagan Informational [Page 12] RFC 7993 CSS Reqs for RFCs December 2016

 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

Flanagan Informational [Page 13] RFC 7993 CSS Reqs for RFCs December 2016

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

Flanagan Informational [Page 14]

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