    Independent Submission                                         R. Gieben
    Request for Comments: 7328                                        Google
    Category: Informational                                      August 2014
    ISSN: 2070-1721

              Writing I-Ds and RFCs Using Pandoc and a Bit of XML

    Abstract

       This document presents a technique for using a Markdown syntax
       variant, called Pandoc, and a bit of XML (as defined in RFC 2629) as
       a source format for documents that are Internet-Drafts (I-Ds) or
       RFCs.

       The goal of this technique (which is called Pandoc2rfc) is to let an
       author of an I-D focus on the main body of text without being
       distracted too much by XML tags; however, it does not alleviate the
       need to typeset some files in XML.

    Status of This Memo

       This document is not an Internet Standards Track specification; it is
       published for informational purposes.

       This is a contribution to the RFC Series, independently of any other
       RFC stream.  The RFC Editor has chosen to publish this document at
       its discretion and makes no statement about its value for
       implementation or deployment.  Documents approved for publication by
       the RFC Editor are not a candidate for any level of Internet
       Standard; see Section 2 of RFC 5741.

       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/rfc7328.

    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.

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    Table of Contents

       1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
       2.  Pandoc to RFC . . . . . . . . . . . . . . . . . . . . . . . .   2
         2.1.  Dependencies  . . . . . . . . . . . . . . . . . . . . . .   5
       3.  Building an Internet-Draft  . . . . . . . . . . . . . . . . .   5
       4.  Supported Features  . . . . . . . . . . . . . . . . . . . . .   5
       5.  Unsupported Features and Limitations  . . . . . . . . . . . .   7
       6.  Pandoc Style  . . . . . . . . . . . . . . . . . . . . . . . .   7
         6.1.  Figures . . . . . . . . . . . . . . . . . . . . . . . . .   7
         6.2.  Tables  . . . . . . . . . . . . . . . . . . . . . . . . .   7
         6.3.  References  . . . . . . . . . . . . . . . . . . . . . . .   7
         6.4.  Index . . . . . . . . . . . . . . . . . . . . . . . . . .   8
       7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
       8.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
       9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
         9.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
         9.2.  Informative References  . . . . . . . . . . . . . . . . .   9
       Appendix A.  Cheat Sheet  . . . . . . . . . . . . . . . . . . . .  10

    1.  Introduction

       This document presents a technique for using a Markdown [Markdown]
       syntax variant, called Pandoc [Pandoc], and a bit of XML [RFC2629] as
       a source format for documents that are Internet-Drafts (I-Ds) or
       RFCs.

       The goal of this technique is to let an author of an I-D focus on the
       main body of text without being distracted too much by XML tags;
       however, it does not alleviate the need to typeset some files in XML.

       Pandoc is a format that is almost plain text and therefore
       particularly well suited for editing RFC-like documents.  The syntax
       itself is a superset of the syntax championed by Markdown.

    2.  Pandoc to RFC

       Pandoc's syntax is easy to learn and write, and it can be translated
       to numerous output formats, including, but not limited to: HTML,
       EPUB, (plain) Markdown, and DocBook XML.

       Pandoc2rfc allows authors to write in Pandoc syntax that is then
       transformed to XML and given to xml2rfc.  The conversions are, in a
       way, amusing, as we start off with (almost) plain text, use elaborate
       XML, and end up with plain text again.

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                 +-------------------+   pandoc   +---------+
                 | ALMOST PLAIN TEXT |   ------>  | DOCBOOK |
                 +-------------------+     1      +---------+
                               |                       |
                 non-existent  |                     2 | xsltproc
                   faster way  |                       |
                               v                       v
                       +------------+    xml2rfc  +---------+
                       | PLAIN TEXT |  <--------  |   XML   |
                       +------------+      3      +---------+

                      Figure 1: Attempt to justify Pandoc2rfc

       The output of step 2 in Figure 1 is XML that is suitable for
       inclusion in either the "middle" or "back" section of an RFC.

       Even though Pandoc2rfc abstracts away a lot of XML details, there are
       still places left where XML files needs to be edited -- most notably
       in the "front" section of an RFC.

       The simplest way to start using Pandoc2rfc is to create a template
       XML file and include the appropriate XML for the "front", "middle",
       and "back" section:

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       <?xml version='1.0' ?>
       <!DOCTYPE rfc SYSTEM 'rfc2629.dtd' [
       <!ENTITY pandocAbstract PUBLIC '' 'abstract.xml'>
       <!ENTITY pandocMiddle   PUBLIC '' 'middle.xml'>
       <!ENTITY pandocBack     PUBLIC '' 'back.xml'>
       <!ENTITY rfc.2629       PUBLIC '' 'reference.RFC.2629.xml'>
       ]>

       <rfc ipr='trust200902' docName='draft-string-example'>
        <front>
           <title>Writing I-Ds and RFCs using Pandoc</title>
           <author>
              <organization/>
              <address><uri>http://www.example.com</uri></address>
           </author>
           <date/>
           <abstract>
               &pandocAbstract;
           </abstract>
       </front>
       <middle>
           &pandocMiddle;
       </middle>
       <back>
           <references title="Normative References">
               &rfc.2629;
           </references>
           &pandocBack;
       </back>
       </rfc>

                         Figure 2: A minimal template.xml

       In this case, you will need to edit four documents:

       1.  "abstract.mkd" - contains the abstract;

       2.  "middle.mkd" - contains the main body of text;

       3.  "back.mkd" - holds the appendices (if any);

       4.  and this "template.xml" -- probably a fairly static file; among
           other things, it holds the author(s) and the references.

       Up-to-date source code for Pandoc2rfc can be found at [Pandoc2rfc];
       this includes the style sheet "transform.xsl", which is used for the
       XML transformation (also see Section 3).

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    2.1.  Dependencies

       Pandoc2rfc needs "xsltproc" [XSLT] and "pandoc" [Pandoc] to be
       installed.  The conversion to xml2rfc XML is done with a style sheet
       based on XSLT version 1.0 [W3C.REC-xslt-19991116].

       When using the template from Figure 2, xml2rfc version 2 (or higher)
       must be used.

    3.  Building an Internet-Draft

       Assuming the setup from Section 2, we can build an I-D as follows (in
       a Unix-like environment):

       for i in abstract middle back; do
       pandoc -st docbook $i.mkd | xsltproc --nonet transform.xsl - > $i.xml
       done

       xml2rfc template.xml -f draft.txt --text  # create text output
       xml2rfc template.xml -f draft.html --html # or create HTML output
       xml2rfc template.xml -f draft.xml --exp   # or create XML output

                             Figure 3: Building an I-D

       Note that the output file names (abstract.xml, middle.xml, and
       back.xml) must match the names used as the XML entities in
       "template.xml".  (See the "!ENTITY" lines in Figure 2.)  The
       Pandoc2rfc source repository includes a shell script that
       incorporates the above transformations.  Creating a "draft.txt" or a
       "draft.xml" can be done with "pandoc2rfc *.mkd" and "pandoc2rfc -X
       *.mkd", respectively.

    4.  Supported Features

       The full description of Pandoc's syntax can be found in
       [PandocGuide].  The following features of xml2rfc are supported by
       Pandoc2rfc (also see Table 1 in Appendix A for a "cheat sheet"):

       o  Sections with an anchor and title attributes;

       o  Several list styles:

          *  style="symbols", use "* " for each item;

          *  style="numbers", use digits: "1. " for each item;

          *  style="empty", use "#. " for each item;

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          *  style="format %i", use lowercase Roman numerals: "ii. ";

          *  style="format (%d)", use uppercase Roman numerals "II. ";

          *  style="format ...", use strike-through text at the start in the
             first element, "1. ~~REQ%d.~~ ";

          *  style="letters", use lower- or uppercase letters: "a.  " and
             "A.  " (note: two spaces as mandated by Pandoc);

          *  style="hanging", use the Pandoc definition list syntax:

             Term 1

             :   Definition 1

       o  Spanx style="verb", style="emph", and style="strong",
          respectively, use: "`text`", "_text_" or "**text**";

       o  Block quote, which is converted to a paragraph within a "<list
          style="empty">";

       o  Figures with an anchor and title (Section 6.1);

       o  Tables with an anchor and title (Section 6.2);

       o  References (Section 6.3)

          *  external ("<eref>");

          *  cross-reference ("<xref>"), to:

             +  sections (handled by Pandoc);

             +  figures (handled by XSLT);

             +  tables (handled by XSLT).

       o  Index, by using footnotes and superscript text (Section 6.4);

       o  Citations, by using cross-references;

       o  Processing Instructions (PIs), which appear as "<?rfc?>", may be
          used after a section header.  They are carried over to the
          generated XML.

       o  The "<vspace>" tag is supported and carried over to the generated
          XML.

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    5.  Unsupported Features and Limitations

       With Pandoc2rfc, an author of an I-D can get a long way without
       needing to input XML, but it is not a 100% solution.  The initial
       setup and the reference library still force the author to edit XML
       files.  The metadata feature (Pandoc's "Title Block" extension) is
       not used in Pandoc2rfc.  This information (authors, date, keyword,
       and URLs) should be put in the "template.xml".

       Some other quirks:

       o  Comments are supported via HTML comments in the Pandoc source
          files.

       o  Citations are supported via cross-references; the citation syntax
          of Pandoc is not used.

       o  Authors still need to know how to deal with possible errors from
          xml2rfc.

    6.  Pandoc Style

       The following sections detail how to use the Pandoc syntax for
       figures, tables, and references to get the desired output.

    6.1.  Figures

       Indent the paragraph with 4 spaces as mandated by Pandoc.  If you add
       an inline footnote _directly_ after the figure, the artwork gets a
       title attribute with the text of that footnote (and a possible
       anchor).

    6.2.  Tables

       A table can be entered by using Pandoc's table syntax.  You can
       choose multiple styles as input, but they all are converted to the
       same style table (plain "<texttable>") in xml2rfc.  If you add an
       inline footnote _directly_ after the table, it will get a title
       attribute with the text of that footnote (and a possible anchor).
       The built-in syntax of Pandoc to create a caption with "Table:"
       should not be used.

    6.3.  References

       Pandoc provides a syntax that can be used for references.  Its syntax
       is repeated in this paragraph.  Any reference like
       "[Click here](URI)" is an external reference.  An internal reference
       (i.e., "see Section X") is typeset with "[](#localid)".

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       For referencing RFCs (and other documents), you will need to add the
       reference source in the template as an external XML entity; Figure 2
       provides an example.  After that, you can use the following syntax to
       create a citation: "[](#RFC2629)" to cite RFC 2629.

       There is no direct support for referencing tables, figures, and
       artworks, but Pandoc2rfc employs the following "hack".  If an inline
       footnote is added after the figure or table, the text of the footnote
       is used as the title.  The first word up until a double colon "::"
       will be used as the anchor.  If a figure has an anchor, it will be
       centered on the page.

       Figure 2, for instance, is followed by this inline footnote:

       ^[fig:minimal::A minimal template.xml.]

    6.4.  Index

       An index can be generated by using the following syntax:

       ^[ ^item^ subitem ]

       where "subitem" is optional.

    7.  Acknowledgements

       The following people have helped shape Pandoc2rfc: Benno Overeinder,
       Erlend Hamnaberg, Matthijs Mekking, and Trygve Laugstoel.

    8.  Security Considerations

       This document raises no security issues.

    9.  References

    9.1.  Normative References

       [RFC2629]  Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
                  June 1999.

       [W3C.REC-xslt-19991116]
                  Clark, J., "XSL Transformations (XSLT) Version 1.0", World
                  Wide Web Consortium Recommendation REC-xslt-19991116,
                  November 1999,
                  <http://www.w3.org/TR/1999/REC-xslt-19991116>.

       [XSLT]     Veillard, D., "The XSLT C library for GNOME", 2006,
                  <http://xmlsoft.org/XSLT/xsltproc2.html>.

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    9.2.  Informative References

       [Markdown] Gruber, J., "Markdown", 2004,
                  <http://daringfireball.net/projects/markdown/>.

       [Pandoc]   MacFarlane, J., "Pandoc, a universal document converter",
                  2006, <http://johnmacfarlane.net/pandoc/>.

       [Pandoc2rfc]
                  Gieben, R., "Pandoc2rfc git repository", October 2012,
                  <http://github.com/miekg/pandoc2rfc>.

       [PandocGuide]
                  MacFarlane, J., "Pandoc User's Guide", 2006,
                  <http://johnmacfarlane.net/pandoc/README.html>.

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    Appendix A.  Cheat Sheet

             +---------------------+-----------------+--------------+
             | Textual construct   | Pandoc syntax   | Text output  |
             +---------------------+-----------------+--------------+
             | Section Header      | "# Section"     | 1. Section   |
             | Unordered List      | "* item"        | o  item      |
             | Unordered List      | "#. item"       | item         |
             | Ordered List        | "1. item"       | 1.  item     |
             | Ordered List        | "a.  item"      | a.  item     |
             | Ordered List        | "ii. item"      | i.  item     |
             | Ordered List        | "II. item"      | (1)  item    |
             | Ordered List        | "A.  item"      | A.  item     |
             | Ordered List        | "1. ~~REQ%d.~~" | REQ1.        |
             | Emphasis            | "_text_"        | _text_       |
             | Strong Emphasis     | "**text**"      | *text*       |
             | Verbatim            | "`text`"        | "text"       |
             | Block Quote         | "> quote"       | quote        |
             | External Reference  | "[Click](URI)"  | Click [1]    |
             | Internal Reference  | "[](#id)"       | Section 1    |
             | Figure Anchor       | "^[fid::text]"  | N/A          |
             | Figure Reference    | "[](#fid)"      | Figure 1     |
             | Table Anchor        | "^[tid::text]"  | N/A          |
             | Table Reference     | "[](#tid)"      | Table 1      |
             | Citations           | "[](#RFC2119)"  | [RFC2119]    |
             | Table               | Tables          | *            |
             | Figures             | Code Blocks     | *            |
             | Definition List     | Definition      | *            |
             | Index               | ^[ ^item^ ]     | *            |
             +---------------------+-----------------+--------------+

       * This construct creates output too voluminous to show in the table.

                Table 1: The most important textual constructs that
                             can be used in Pandoc2rfc

    Author's Address

       R. (Miek) Gieben
       Google

       EMail: miek@google.com

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