Network Working Group N. Brownlee (Ed.) Internet-Draft The University of Auckland Intended status: Informational IAB Expires: August 16, 2014 February 12, 2014 SVG Drawings for RFCs: SVG 1.2 RFC draft-brownlee-svg-rfc-02 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 This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on August 16, 2014. Copyright Notice Copyright (c) 2014 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. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Brownlee (Ed.) & IAB Expires August 16, 2014 [Page 1] Internet-Draft SVG Drawings for RFCs: SVG 1.2 RFC February 2014 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. Sequence Digrgams . . . . . . . . . . . . . . . . . . . . 4 4.2. State Diagrams . . . . . . . . . . . . . . . . . . . . . 6 4.3. Packet Layout Diarrams . . . . . . . . . . . . . . . . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 7. Revision History [RFC Editor please delete] . . . . . . . . . 6 8. Appendix: Elements and attributes allowed in SVG 1.2 RFC . . 7 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 9.1. Normative References . . . . . . . . . . . . . . . . . . 9 9.2. Informative References . . . . . . . . . . . . . . . . . 9 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 Brownlee (Ed.) & IAB Expires August 16, 2014 [Page 2] Internet-Draft SVG Drawings for RFCs: SVG 1.2 RFC February 2014 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. Brownlee (Ed.) & IAB Expires August 16, 2014 [Page 3] Internet-Draft SVG Drawings for RFCs: SVG 1.2 RFC February 2014 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 This section presents some examples of possible language(s) which could be used to create several kinds of diagrams that are common in RFCs. 4.1. Sequence Digrgams Example: Figure 6 from draft-loreto-httpbis-trusted-proxy20-00. column 1 width 250 # columns have vertical line to bottom text above "user-agent" column 2 width 250 text "Proxy" column 3 # Last col text "Server" object 1 # Only need polylines pline 1 to 2, arrowhead at end text above "(1) TLS ClientHello" text below "(ALPN ProtocolName: http)" Brownlee (Ed.) & IAB Expires August 16, 2014 [Page 4] Internet-Draft SVG Drawings for RFCs: SVG 1.2 RFC February 2014 object 2 pline 1 to 2, arrowhead at start text above "(2) TLS Error" text below "(Proxy Cert)" object 3 pline 1 to 1.3, down, back to 1, arrowhead at end text seg 2 centre "(inform user of the SecureProxy)" #object 4 # block 1 to 2, objects 5 to 6, grey # text above "Extra block" object 5 pline 1 to 2, arrowhead at end text above "(3) TLS ClientHello" object 6 pline 1 to 2, arrowhead at start text above "(4) ServerHello" object 7 blank 1 to 2 object 8 block 1 to 2, objects 8 to 16, "grey" text above "HTTP2.0" object 9 pline 1 to 2, arrowhead at end text seg 1 centre "(5) stream(X) GET" object 10 pline 2 to 3, arrowhead at end text seg 1 above "(6) TLS ClientHello" object 11 pline 2 to 3, arrowhead at start text seg 1 above "TLS ServerHello" object 12 blank 2 to 3 object 13 block 2 to 3, objects 13 to 16, grey text seg 1 above "HTTP2.0" object 14 Brownlee (Ed.) & IAB Expires August 16, 2014 [Page 5] Internet-Draft SVG Drawings for RFCs: SVG 1.2 RFC February 2014 pline 2 to 3, arrowhead at end text seg 1 centre "(7) stream(Z) GET" object 15 pline 2 to 3, arrowhead at start text seg 1 centre "(8) stream(Z) 200 OK" object 16 pline 1 to 2, arrowhead at start text seg 1 centre "(9) stream(X) 200 OK" The SVG diagram produced from this can be seen at https://www.cs.auckland.ac.nz/~nevil/http-proxy-dwg.svg 4.2. State Diagrams 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. 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. Added most attributes and elements to the Appendix. version -02, 12 Feb 14: Added metalanguage example to make time-sequence drawings. Brownlee (Ed.) & IAB Expires August 16, 2014 [Page 6] Internet-Draft SVG Drawings for RFCs: SVG 1.2 RFC February 2014 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. , the list of allowed colours, is a black-and-white subset of the SVG colour names. Elements: svg (version, baseProfile=tiny, width, viewBox, preserveAspectRatio, snapshotTime) g defs title desc use (x, y, xlink:href) 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 Brownlee (Ed.) & IAB Expires August 16, 2014 [Page 7] Internet-Draft SVG Drawings for RFCs: SVG 1.2 RFC February 2014 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) (black, grey, darkgrey, dimgrey, lightgrey, gray, darkgray, dimgray, lightgray, white) opacity solid-opacity solid-color (currentColor, ) color (currentColor, ) stop-color (currentColor, ) 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 Brownlee (Ed.) & IAB Expires August 16, 2014 [Page 8] Internet-Draft SVG Drawings for RFCs: SVG 1.2 RFC February 2014 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, . [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, . 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, . Authors' Addresses Nevil Brownlee The University of Auckland EMail: n.brownlee@auckland.ac.nz Internet Architecture Board EMail: iab@iab.org Brownlee (Ed.) & IAB Expires August 16, 2014 [Page 9]