Network Working Group N. Brownlee (Ed.)
Internet-Draft The University of Auckland
Intended status: Informational IAB
Expires: August 15, 2014
February 11, 2014
SVG Drawings for RFCs: SVG 1.2 RFC
draft-brownlee-svg-rfc-01
Abstract
This document specifies SVG 1.2 RFC - an SVG profile for use in
diagrams that may appear in RFCs - and considers some of the issues
concerning the creation and use of such diagrams.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. SVG 1.2 RFC: An SVG profile for RFCs . . . . . . . . . . . . 2
3. How to create SVG drawings . . . . . . . . . . . . . . . . . 4
4. Meta-language for diagrams common in RFCs . . . . . . . . . . 4
4.1. State Diagrams . . . . . . . . . . . . . . . . . . . . . 4
4.2. Sequence Digrgams . . . . . . . . . . . . . . . . . . . . 4
4.3. Packet Layout Diarrams . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
7. Revision History [RFC Editor please delete] . . . . . . . . . 4
8. Appendix: Elements and attributes allowed in SVG 1.2 RFC . . 5
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . 7
1. Introduction
Over the last two years the RFC Editor has worked with the Internet
community to develop specifications for changes in the format of
RFCs. An outline of the resulting specifications was published as
[RFC6949] in May 2013. Since then a Design Team has been working
with the RFC Editor to flesh out those specifications. One aspect of
the changes is to allow line drawings in RFCs; [RFC6949] says
"Graphics may include ASCII art and a more complex form to be
defined, such as SVG line art [SVG]. Color and grayscale will not
be accepted. RFCs must correctly display in monochromatic black-
and-white to allow for monochrome displays, black-and- white
printing, and support for visual disabilities."
SVG (Scalable Vector Graphics) has been developed by W3C, the World
Wide Web Consortium; its current standard is SVG 1.1 Full
[W3C.REC-SVG11-20110816]. This document defines SVG 1.2 RFC, an SVG
profile (i.e. a subset of SVG) that is suitable for RFC line
drawings.
Note that in RFCs, the text provides normative descriptions of
protocols, systems, etc. Diagrams may be used to help explain
concepts more clearly, but they are informative, not normative.
2. SVG 1.2 RFC: An SVG profile for RFCs
As a starting point for SVG 1.2 RFC, the Design Team decided to use
SVG 1.2 Tiny [W3C.REC-SVGTiny12-20081222]. SVG 1.2 Tiny is an SVG
subset intended to be implemented on small, mobile devices such as
cellphones and smartphones. That should allow RFCs to be rendered
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well on such devices, especially those that have small screens.
However, RFCs are self-contained documents that do not change once
they are published. The use of SVG drawings in RFCs is intended to
allow authors to create drawings that are simple to produce, and
easier to understand than our traditional 'ASCII Art' ones. In
short, we are also trying to improve access to the content in RFCs,
so SVG drawings need to be kept as simple as possible.
SVG can provide a complete User Interface, but within RFCs, all we
need are simple diagrams that do not change once the RFC is
published. Therefore, SVG RFC does not allow anything from the
following sections in SVG Tiny 1.2 [W3C.REC-SVGTiny12-20081222]:
12 Multimedia
13 Interactivity
15 Scripting
16 Animation
18 Metadata
19 Extensibility
Note that SVG Tiny 1.2 elements may have many properties or
attributes that are needed to support aspects of the above sections.
Those are not allowed in SVG 1.2 RFC.
Considering the other sections in SVG Tiny 1.2
[W3C.REC-SVGTiny12-20081222]:
9 Basic Shapes
10 Text
Everything in these sections is allowed in SVG 1.2 RFC.
11 Painting: Filling, Stroking, Colors and Paint Servers
Anything relating to 'color' is not allowed in SVG 1.2 RFC,
everything else is allowed.
14 Linking
SVG Tiny 1.2 allows internationalized IRIs in references. In
SVG 1.2 RFC such links must be ASCII only. That should not
cause problems, since one can just use the URI form of any IRI.
Authors should try to use links only to URIs that are long-trem
stable.
17 Fonts
SVG 1.2 RFC only allows 'serif', 'sans-serif' and 'monospace'
generic font families from the WebFonts facility, described in
CSS 2.1 [W3C.REC-CSS2-20110607], section 15, Fonts. In
particular, the SVG 'font' element is not allowed.
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3. How to create SVG drawings
Many drawing packages can be used to create SVG drawings, for example
Open Source packages Inkscape and Dia. Be aware that such packages
may use SVG elements or attributes that are not allowed in SVG 1.2
RFC. For example, the 'marker' attribute is often used to place
symbols such as arrowheads on lines, but 'marker' is not allowed in
SVG 1.2 Tiny or SVG 1.2 RFC. In such cases one has to draw the
arrowhead in another, simpler way.
We will need to provide a tool to check that a diagram only uses
elements and attributes that are allowed in SVG 1.2 RFC. These are
listed in the Appendix below. [Need to take the lists from SVG Tiny
1.2 and prune them for SVG 1.2 RFC. TBD]
Diagrams produced with these packages may produce large SVG files
that are hard to read or understand directly. We should provide a
tool to strip out unnecccessary attributes; authors could run that
tool over their drawings, and see whether such stripping causes any
visible changes.
Another way to create SVG drawings is to write programs to draw them.
For example, using python and its svgwrite module is a pleasant
environment (for those who like writing code).
4. Meta-language for diagrams common in RFCs
4.1. State Diagrams
4.2. Sequence Digrgams
4.3. Packet Layout Diarrams
5. IANA Considerations
This document does not create a new registry nor does it register any
values in existing registries; no IANA action is required.
6. Acknowledgements
Thanks to the Design Team members for their helpful comments and
suggestions for SVG 1.2 RFC.
7. Revision History [RFC Editor please delete]
version -00, 29 Jan 14:
Initial version, using content from Nevil's
emails to the Design Team.
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version -01, 11 Feb 14:
Allow links to 'long-term stable URIs'
Link URIs must be ASCII only
Need for tools to check SVG 1.2 RFC compatibilty and to strip
'unneccessary' attributes explicitly stated.
Statement that drawings can't be normative removed; Postscript-
only RFCs already exist.
8. Appendix: Elements and attributes allowed in SVG 1.2 RFC
Elements, properties and attributes selected for SVG 1.2 RFC from
[W3C.REC-SVGTiny12-20081222].
In the list below, elements and properties are listed on the
left,and their allowed values are given in parentheses on the
right.
<color>, the list of allowed colours, is a black-and-white
subset of the SVG colour names.
Elements:
rect (x, y, width, height, rx, ry)
circle (cx, cy, r)
ellipse (cx, cy, rx, ry)
line (x1, y1, x2, y2)
polyline (points)
polygon (points)
text (x, y, rotate)
tspan
textArea (x, y, width, height, auto)
tbreak
solidcolor
linearGradient (gradientUnits, x1, y1, x2, y2)
radialGradient (gradientUnits, cx, cy, r)
stop (offset)
Properties: (most allow inherit as a value)
stroke
stroke-width
stroke-linecap (butt, round, square)
stroke-linejoin (miter, round, bevel)
stroke-mitrelimit
stroke-dasharray
stroke-dashoffset
stroke-opacity
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vector-effect (non-scaling-stroke, none)
viewport-fill (none, currentColor)
viewport-fill-opacity
display (inline, block, list-item, run-in, compact,
marker, table, inline-table, table-row-group,
table-header-group, table-footer-group,
table-row, table-column-group,
table-column, table-cell, table-caption,
none)
visibility (visible, hidden, collapse)
color-rendering (auto, optimizeSpeed, optimizeQuality)
shape-rendering (auto, optimizeSpeed, crispEdges,
geometricPrecision)
text-rendering (auto, optimizeSpeed, optimizeLegibility,
geometricPrecision)
buffered-rendering (auto, dynamic, static)
<color> (black, grey, darkgrey, dimgrey, lightgrey,
gray, darkgray, dimgray, lightgray, white)
opacity
solid-opacity
solid-color (currentColor, <color>)
color (currentColor, <color>)
stop-color (currentColor, <color>)
stop-opacity
line-increment (auto)
text-align (start,end, center)
display-align (auto, before, center, after)
font-size
font-family (serif, sans-serif, monospace)
font-weight (normal, bold, bolder, lighter)
font-style (normal, italic, oblique)
font-variant (normal, small-caps)
direction (ltr, rtl)
unicode-bidi (normal, embed, bidi-override)
text-anchor (start, middle, end)
fill (none, black or grey)
fill-rule (nonzero, evenodd)
fill-opacity
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9. References
9.1. Normative References
[RFC6949] Flanagan, H. and N. Brownlee, "RFC Series Format
Requirements and Future Development", RFC 6949, May 2013.
[W3C.REC-SVGTiny12-20081222]
Grasso, A., Ferraiolo, J., Neumann, A., Jackson, D.,
Berjon, R., Schepers, D., Lilley, C., McCormack, C.,
Hardy, V., Emmons, A., Hayman, S., Dahlstroem, E.,
Shellshear, A., Ramani, N., Northway, C., Andersson, O.,
and A. Quint, "Scalable Vector Graphics (SVG) Tiny 1.2
Specification", World Wide Web Consortium Recommendation
REC-SVGTiny12-20081222, December 2008,
<http://www.w3.org/TR/2008/REC-SVGTiny12-20081222>.
[W3C.REC-CSS2-20110607]
Celik, T., Hickson, I., Bos, B., and H. Lie, "Cascading
Style Sheets Level 2 Revision 1 (CSS 2.1) Specification",
World Wide Web Consortium Recommendation REC-
CSS2-20110607, June 2011,
<http://www.w3.org/TR/2011/REC-CSS2-20110607>.
9.2. Informative References
[W3C.REC-SVG11-20110816]
Dahlstroem, E., Dengler, P., Grasso, A., Lilley, C.,
McCormack, C., Schepers, D., Watt, J., Ferraiolo, J.,
Fujisawa, J., and D. Jackson, "Scalable Vector Graphics
(SVG) 1.1 (Second Edition)", World Wide Web Consortium
Recommendation REC-SVG11-20110816, August 2011,
<http://www.w3.org/TR/2011/REC-SVG11-20110816>.
Authors' Addresses
Nevil Brownlee
The University of Auckland
EMail: n.brownlee@auckland.ac.nz
Internet Architecture Board
EMail: iab@iab.org
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