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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
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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]