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IETF RFC 7993
Last modified on Friday, December 16th, 2016
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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/RFC 7993.
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 [RFC 7992], 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 [RFC 7990].
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 [RFC 7992].
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" [RFC 7322] and "RFC
Streams, Headers, and Boilerplates" [RFC 7841].
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>.
[RFC 7841] Halpern, J., Ed., Daigle, L., Ed., and O. Kolkman, Ed.,
"RFC Streams, Headers, and Boilerplates", RFC 7841, DOI
10.17487/RFC 7841, May 2016,
<http://www.rfc-editor.org/info/RFC 7841>.
[RFC 7322] Flanagan, H. and S. Ginoza, "RFC Style Guide", RFC 7322,
DOI 10.17487/RFC 7322, September 2014,
<http://www.rfc-editor.org/info/RFC 7322>.
[RFC 7990] Flanagan, H., "RFC Format Framework", RFC 7990,
DOI 10.17487/RFC 7990, December 2016,
<http://www.rfc-editor.org/info/RFC 7990>.
[RFC 7992] Hildebrand, J., Ed. and P. Hoffman, "HTML Format for
RFCs", RFC 7992, DOI 10.17487/RFC 7992, December 2016,
<http://www.rfc-editor.org/info/RFC 7992>.
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
RFC TOTAL SIZE: 18990 bytes
PUBLICATION DATE: Friday, December 16th, 2016
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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