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Internet Architecture Board (IAB)                            H. FlanaganRequest for Comments: 7993                                    RFC EditorCategory: Informational                                    December 2016ISSN: 2070-1721Cascading Style Sheets (CSS) Requirements for RFCsAbstract   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; seeSection 2 of RFC 7841.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://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 toBCP 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 2016Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .32.  Design Goal . . . . . . . . . . . . . . . . . . . . . . . . .33.  General Requirements  . . . . . . . . . . . . . . . . . . . .34.  Page Layout . . . . . . . . . . . . . . . . . . . . . . . . .44.1.  Title Page Header . . . . . . . . . . . . . . . . . . . .44.2.  Body  . . . . . . . . . . . . . . . . . . . . . . . . . .44.3.  Font Choices  . . . . . . . . . . . . . . . . . . . . . .45.  Printing  . . . . . . . . . . . . . . . . . . . . . . . . . .46.  Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . .57.  CSS Classes and Attributes  . . . . . . . . . . . . . . . . .57.1.  .alignCenter  . . . . . . . . . . . . . . . . . . . . . .57.2.  .alignRight . . . . . . . . . . . . . . . . . . . . . . .57.3.  .artwork  . . . . . . . . . . . . . . . . . . . . . . . .57.3.1.  .art-ascii-art  . . . . . . . . . . . . . . . . . . .57.3.2.  .art-logo . . . . . . . . . . . . . . . . . . . . . .57.4.  .cref . . . . . . . . . . . . . . . . . . . . . . . . . .57.5.  .crefAnchor . . . . . . . . . . . . . . . . . . . . . . .67.6.  .crefSource . . . . . . . . . . . . . . . . . . . . . . .67.7.  .dlCompact  . . . . . . . . . . . . . . . . . . . . . . .67.8.  .dlHanging  . . . . . . . . . . . . . . . . . . . . . . .67.9.  .dlParallel . . . . . . . . . . . . . . . . . . . . . . .67.10. .docInfo  . . . . . . . . . . . . . . . . . . . . . . . .67.11. .eref . . . . . . . . . . . . . . . . . . . . . . . . . .67.12. .finalized  . . . . . . . . . . . . . . . . . . . . . . .67.13. .note . . . . . . . . . . . . . . . . . . . . . . . . . .67.13.1.  .rfcEditorRemove . . . . . . . . . . . . . . . . . .67.14. .olCompact  . . . . . . . . . . . . . . . . . . . . . . .77.15. .olPercent  . . . . . . . . . . . . . . . . . . . . . . .77.16. .pilcrow  . . . . . . . . . . . . . . . . . . . . . . . .77.17. .relref . . . . . . . . . . . . . . . . . . . . . . . . .77.18. .rendered . . . . . . . . . . . . . . . . . . . . . . . .77.19. .sourcecode . . . . . . . . . . . . . . . . . . . . . . .77.20. .toc  . . . . . . . . . . . . . . . . . . . . . . . . . .77.21. .type . . . . . . . . . . . . . . . . . . . . . . . . . .77.22. .ulCompact  . . . . . . . . . . . . . . . . . . . . . . .87.23. .ulEmpty  . . . . . . . . . . . . . . . . . . . . . . . .87.24. .url  . . . . . . . . . . . . . . . . . . . . . . . . . .87.25. .xref . . . . . . . . . . . . . . . . . . . . . . . . . .88.  Security Considerations . . . . . . . . . . . . . . . . . . .89.  References  . . . . . . . . . . . . . . . . . . . . . . . . .89.1.  Normative References  . . . . . . . . . . . . . . . . . .89.2.  Informative References  . . . . . . . . . . . . . . . . .9Appendix A.  List of Classes  . . . . . . . . . . . . . . . . . .10   IAB Members at the Time of Approval . . . . . . . . . . . . . . .14   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .14   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .14Flanagan                      Informational                     [Page 2]

RFC 7993                    CSS Reqs for RFCs              December 20161.  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 20164.  Page Layout4.1.  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 20166.  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 inAppendix 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 20167.5.  .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 20167.14.  .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 inRFC 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 20167.22.  .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.  References9.1.  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 20169.2.  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 2016Appendix A.  List of Classes   This section lists all the CSS classes.  Except for those also listed   inSection 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  .crefFlanagan                      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  .leftFlanagan                      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  .selfRefFlanagan                      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  .vcardFlanagan                      Informational                    [Page 13]

RFC 7993                    CSS Reqs for RFCs              December 2016IAB 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 WoolfAcknowledgements   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/0000-0002-2647-2220Flanagan                      Informational                    [Page 14]