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.

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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

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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.

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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.

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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.

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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.

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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.

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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>.

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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>.

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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

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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

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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

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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

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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: [email protected]

URI: http://orcid.org/0000-0002-2647-2220

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