RFC 7993 INFORMATIONAL RFC FORMAT · CSS · ACCESSIBILITY
Cascading Style Sheets (CSS) Requirements for RFCs
Requirements for the default style sheet used in RFC HTML publications.
RFC EDITOR
Flanagan, H., "Cascading Style Sheets (CSS) Requirements for RFCs", RFC 7993, DOI 10.17487/RFC7993, December 2016, <https://www.rfc-editor.org/info/rfc7993>.
BIBTEX
@misc{rfc7993,
series = {Request for Comments},
number = 7993,
howpublished = {RFC 7993},
publisher = {RFC Editor},
doi = {10.17487/RFC7993},
url = {https://www.rfc-editor.org/info/rfc7993},
author = {H. Flanagan},
title = {{Cascading Style Sheets (CSS) Requirements for RFCs}},
pagetotal = 14,
year = 2016,
month = dec,
} RFC text
Contents
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.
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
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.
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.
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.
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.
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.
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>.
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>.
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
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
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
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
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
ISO Plain Language
On this page
PROBLEMRFC HTML uses a series-specific CSS style sheet, and the default styles need shared requirements for accessibility, responsive layouts and printing.
MECHANISMThe memo specifies layout, font, printing and list requirements, then defines appearance guidance for selected classes used by RFC HTML.
STATUS TODAYRFC 7993 is an Informational document and the supplied metadata says RFC 9920 updates it.
§1Purpose and Scope
RFC 7992 defines the HTML format for RFCs and assigns visual styling to a CSS style sheet for the RFC Series. The RFC Editor embeds default CSS in published HTML, and readers can override it locally.
RFC 7993 sets requirements for that default style sheet. It says styling should not visibly change the natural-language content unless a requirement says otherwise, and notes that the details may change as publishing tools develop.
This memo sets requirements for the default CSS in RFC HTML pages. It says style rules should not change the document's words or meaning.
§3Design Goal and General Requirements
The design goal is for RFCs to adapt to a wide variety of devices and displays, remain accessible to assisted readers and print correctly. The CSS must support the semantic HTML defined by RFC 7992.
The style sheet should follow W3C accessibility and mobile-device guidance and allow a broad range of internationalized scripts. The page header must include information described by the RFC Style Guide and the RFC streams document.
The page should work on different screen sizes, with assistive tools and on paper. It should also support many writing systems.
§6Layout, Fonts, Printing and Lists
Examples, code and ASCII art use fixed-width fonts; text reflows on smaller screens and has a limited maximum width. Block quotes are indented, tables can show distinct header rows and links are clearly distinguished.
The default web font is sans-serif with broad Unicode support, while print uses a serif font. The embedded style sheet includes printer-friendly rules, and lists have ample spacing unless a compact class is used.
Text must fit smaller screens, and code must use fixed-width fonts. Links, tables and lists need clear formatting, and the embedded CSS must include print styles.
§7How Selected CSS Classes Appear
The memo gives appearance requirements for classes used in RFC HTML. For example, .pilcrow appears at the end of a paragraph, artwork or source-code segment when pointed at, but not in printed output or copied text.
Compact list classes use less spacing, while classes such as .eref, .relref, .url and .xref must be clearly distinguishable as links. The .docInfo, .finalized and .rendered classes are hidden from visible content.
CSS classes identify things such as links, paragraph marks and compact lists. This section says which classes change appearance and how they should look.
§8Security Considerations
The RFC notes that CSS can introduce vulnerabilities such as CSS injection attacks. It requires the CSS used for RFC pages to comply with current W3C CSS specifications to avoid or mitigate attack vectors.
CSS can create security vulnerabilities. The style sheet must follow current W3C CSS specifications to reduce that risk.