Writing I-Ds and RFCs using XML

Status of this Memo

This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited.

Copyright Notice

Copyright © The Internet Society (1999).

Abstract

This memo presents a technique for using XML (Extensible Markup Language) as a source format for documents in the Internet-Drafts (I-Ds) and Request for Comments (RFC) series.

Table of Contents

1.  Introduction
2.  Using the DTD to Write I-Ds and RFCs
    2.1.  XML basics
    2.2.  Front matter
        2.2.1.  The title Element
        2.2.2.  The author Element
        2.2.3.  The date Element
        2.2.4.  Meta Data Elements
        2.2.5.  The abstract Element
        2.2.6.  The note Element
        2.2.7.  Status, Copyright Notice, Table of Contents
        2.2.8.  Everything in the Front
    2.3.  The Middle
        2.3.1.  The section Element
    2.4.  Back matter
        2.4.1.  The references Element
        2.4.2.  Appendices
        2.4.3.  Copyright Status
3.  Processing the XML Source File
    3.1.  Editing
        3.1.1.  Checking
    3.2.  Converting to Text Format
    3.3.  Converting to HTML Format
    3.4.  Viewing
    3.5.  Searching
4.  Security Considerations
5.  References
Appendix A.  The rfc Element
Appendix B.  The RFC DTD
Appendix C.  Acknowledgements
§  Index
§  Author's Address
§  Intellectual Property and Copyright Statements

1.  Introduction

This memo describes how to write a document for the I-D and RFC series using the Extensible Markup Language (World Wide Web Consortium, “Extensible Markup Language (XML) 1.0,” February 1998.) [1] (XML). This memo has three goals:

1. To describe a simple XML Document Type Definition (DTD) that is powerful enough to handle the simple formatting requirements of RFC-like documents whilst allowing for meaningful markup of descriptive qualities.
2. To describe software that processes XML source files, including a tool that produces documents conforming to RFC 2223 (Postel, J. and J. Reynolds, “Instructions to RFC Authors,” October 1997.) [2], HTML format, and so on.
3. To provide the proof-of-concept for the first two goals (this memo was written using this DTD and produced using that software).

It is beyond the scope of this memo to discuss the political ramifications of using XML as a source format for RFC-like documents. Rather, it is simply noted that adding minimal markup to plain text:

• allows the traditional production of textual RFC-like documents using familiar editors;
• requires some, albeit minimal, additions to existing software environments; and,
• permits information to be organized, searched, and retrieved using both unstructured and structured mechanisms.

2.  Using the DTD to Write I-Ds and RFCs

We do not provide a formal or comprehensive description of XML. Rather, this section discusses just enough XML to use a Document Type Declaration (DTD) to write RFC-like documents.

If you're already familiar with XML, skip to Appendix B (The RFC DTD) to look at the DTD.

2.1.  XML basics

There are very few rules when writing in XML, as the syntax is simple. There are five terms you'll need to know:

1. An "element" usually refers to a start tag, an end tag, and all the characters in between, e.g., "<example>text and/or nested elements</example>"
2. An "empty element" combines the start tag and the end tag, e.g., "<empty/>". You don't find these in HTML.
3. An "attribute" is part of an element. If present, they occur in the start tag, e.g., "<example name='value'>". Of course, they can also appear in empty elements, e.g., "<empty name='value'/>".
4. An "entity" is a textual macro that starts with "&". Don't worry about these, you'll only use them whenever you want to put a "&" or a "<" in your text.
5. A "token" is a string of characters. The first character is either a letter or an underscore ("_"). Any characters that follow are either letters, numbers, an underscore, or a period (".").

First, start your source file with an XML declaration, a reference to the DTD, and the "rfc" element:

    <?xml version="1.0"?>
    <!DOCTYPE rfc SYSTEM "rfcXXXX.dtd">
    <rfc>
        ...
    </rfc>

Ignore the first two lines -- the declaration and the reference -- and simply treat them as opaque strings. Nothing else should be present after the "</rfc>" tag.

Second, make sure that all elements are properly matched and nested. A properly matched element that starts with "<example>" is eventually followed with "</example>". (Empty elements are always matched.) Elements are properly nested when they don't overlap.

For example,

    <outer>
        ...
        <inner>
            ...
        </inner>
        ...
    </outer>

is properly nested.

However,

    <outer>
        ...
        <inner>
            ...
        </outer>
        ...
    </inner>

overlaps, so the elements aren't properly nested.

Third, never use "<" or "&" in your text. Instead, use either "&lt;" or "&amp;", respectively.

Fourth, there are two quoting characters in XML, 'apostrophe' and "quotation". Make sure that all attributes values are quoted, e.g., "<example name='value'>", If the value contains one of the quoting characters, then use the other to quote the value, e.g., "<example name='"'>", If the value contains both quoting characters, then use one of them to quote the value, and replace occurrances of that character in the attribute value with either '&apos;' (apostrophe) or "&quot;" (quotation), e.g., "<example name='"&apos;"'>".

If you want to put a comment in your source file, here's the syntax:

        <!-- comments can be multiline,
         if you wish -->

Finally, XML is case sensitive.

2.2.  Front matter

Immediately following the "<rfc>" tag is the "front" element:

    <?xml version="1.0"?>
    <!DOCTYPE rfc SYSTEM "rfcXXXX.dtd">
    <rfc>
        <front>
            <title ...>
            <author ...>
            <author ...>
            <date ...>
            <area ...>
            <workgroup ...>
            <keyword ...>
            <keyword ...>
            <abstract ...>
            <note ...>
        </front>
        ...
    </rfc>

(Note that in all examples, indentation is used only for expository purposes.)

The "front" element consists of a "title" element, one or more "author" elements, a "date" element, one or more optional "area" elements, one or more optional "workgroup" elements, one or more optional "keyword" elements, an optional "abstract" element. and, one or more optional "note" elements.

2.2.1.  The title Element

The "title" element identifies the title of the document. Because the title will be used in the headers of the document when formatted according to [2] (Postel, J. and J. Reynolds, “Instructions to RFC Authors,” October 1997.), if the title is more than 42 characters, then an abbreviation should also be provided, e.g.,

    <title abbrev="Much Ado about Nothing">
    The IETF's Discussion on "Source Format of RFC Documents"
    </title>

2.2.2.  The author Element

Each "author" element identifies a document author. Since a document may have more than one author, more than one "author" element may be present. If the author is a person, then three attributes must be present in the "<author>" tag, "initials", "surname", and "fullname", e.g.,

    <author initials="M.T." surname="Rose"
            fullname="Marshall T. Rose">

The "author" element itself consists of an "organization" element, and, an optional "address" element.

The "organization" element is similar to the "title" element, in that an abbreviation may be paired with a long organization name using the "abbrev" attribute, e.g.,

    <organization abbrev="ISI">
        USC/Information Sciences Institute
    </organization>

The "address" element consists of an optional "postal" element, an optional "phone" element, an optional "facsimile" element, an optional "email" element, and, an optional "uri" element.

The "postal" element contains one or more "street" elements, followed by any combination of "city", "region" (state or province), "code" (zipcode or postal code), and "country" elements, e.g.,

    <postal>
        <street>660 York Street</street>
        <street>M/S 40</street>
        <city>San Francisco</city> <region>CA</region>
        <code>94110</code>
        <country>US</country>
    </postal>

This flexibility is provided to allow for different national formats for postal addresses. Note however, that although the order of the "city", "region", "code", and "country" elements isn't specified, at most one of each may be present. Regardless, these elements must not be re-ordered during processing by an XML application (e.g., display applications must preserve the ordering of the information contained in these elements). Finally, the value of the "country" element should be a two-letter code from ISO 3166.

The "phone", "facsimile", "email", and "uri" elements are simple, e.g.,

    <phone>+1 415 695 3975</phone>
    <email>mrose@not.invisible.net</email>
    <uri>invisible.net/</uri>

2.2.3.  The date Element

The "date" element identifies the publication date of the document. It consists of a month and a year, e.g.,

    <date month="February" year="1999" />

The "date" element also has an optional day attribute.

2.2.4.  Meta Data Elements

The "front" element may contain meta data -- the content of these elements does not appear in printed versions of the document.

A document has one or more optional "area", "workgroup" and "keyword" elements, e.g.,

    <area>General</area>
    <workgroup>RFC Beautification Working Group</workgroup>
    <keyword>RFC</keyword>
    <keyword>Request for Comments</keyword>
    <keyword>I-D</keyword>
    <keyword>Internet-Draft</keyword>
    <keyword>XML</keyword>
    <keyword>Extensible Markup Language</keyword>

The "area" elements identify a general category for the document (e.g., one of "Applications", "General", "Internet", "Management", "Operations", "Routing", "Security", "Transport", or "User"), while the "workgroup" elements identify the IETF working groups that produced the document, and the "keyword" elements identify useful search terms.

2.2.5.  The abstract Element

A document may have an "abstract" element, which contains one or more "t" elements (The t Element). In general, only a single "t" element is present, e.g.,

    <abstract>
        <t>This memo presents a technique for using XML
        (Extensible Markup Language) as a source format
        for documents in the Internet-Drafts (I-Ds) and
        Request for Comments (RFC) series.</t>
    </abstract>

2.2.6.  The note Element

A document may have one or more "note" elements, each of which contains one or more "t" elements (The t Element). There is a mandatory "title" attribute. In general, the "note" element contains text from the IESG, e.g.,

    <note title="IESG Note">
        <t>The IESG has something to say.</t>
    </note>

2.2.7.  Status, Copyright Notice, Table of Contents

Note that text relating to the memo's status, copyright notice, or table of contents is not included in the document's markup -- this is automatically inserted by an XML application when it produces either a text or HTML version of the document.

2.2.7.1.  Conformance with RFC 2026

If an Internet-Draft is being produced, then the "ipr" attribute should be present in the "<rfc>" tag at the beginning of the file. The value of the attribute should be one of:

full2026:

indicating that the document is in full conformance with all the provisions of Section 10 of RFC 2026;

noDerivativeWorks2026:

indicating that the document is in full conformance with all the provisions of Section 10 of RFC 2026 except that the right to produce derivative works is not granted; or,

none:

indicating that the document is NOT offered in accordance with Section 10 of RFC 2026, and the author does not provide the IETF with any rights other than to publish as an Internet-Draft.

In the latter case, a copyright notice will not be automatically inserted during processing by an XML application.

Consult [3] (Bradner, S., “The Internet Standards Process -- Revision 3,” October 1996.) for further details.

Finally, if the Internet-Draft is being submitted to an automated process, then the "docName" attribute should be present in the "<rfc>" tag at the beginning of the file. The value of this attribute contains the document (not file) name associated with this Internet-Draft, e.g.,

    <rfc ipr="full" docName="draft-mrose-writing-rfcs-01">
        ...
    </rfc>

2.2.8.  Everything in the Front

So, putting it all together, we have, e.g.,

    <front>
        <title>Writing I-Ds and RFCs using XML</title>

        <author initials="M.T." surname="Rose"
                fullname="Marshall T. Rose">
            <organization>Invisible Worlds, Inc.</organization>

            <address>
                <postal>
                    <street>660 York Street</street>
                    <street>M/S 40</street>
                    <city>San Francisco</city> <region>CA</region>
                    <code>94110</code>
                    <country>US</country>
                </postal>

                <phone>+1 415 695 3975</phone>
                <email>mrose@not.invisible.net</email>
                <uri>invisible.net/</uri>
            </address>
        </author>

        <date month="February" year="1999" />

        <area>General</area>
        <workgroup>RFC Beautification Working Group</workgroup>
        <keyword>RFC</keyword>
        <keyword>Request for Comments</keyword>
        <keyword>I-D</keyword>
        <keyword>Internet-Draft</keyword>
        <keyword>XML</keyword>
        <keyword>Extensible Markup Language</keyword>
        <abstract>
            <t>This memo presents a technique for using XML
            (Extensible Markup Language) as a source format
            for documents in the Internet-Drafts (I-Ds) and
            Request for Comments (RFC) series.</t>
        </abstract>
    </front>

2.3.  The Middle

The "middle" element contains all the sections of the document except for the bibliography and appendices:

    ...
    </front>
    <middle>
        <section ...>
        <section ...>
        <section ...>
    </middle>
    <back>
    ...

The "middle" element consists of one or more "section" elements.

2.3.1.  The section Element

Each "section" element contains a section of the document. There is a mandatory attribute, "title", that identifies the title of the section. There is also an optional attribute, "anchor", that is used for cross-referencing with the "xref" element (The xref Element), e.g.,

    <section anchor="intro" title="Introduction">
        ...
    </section>

The "section" element is recursive -- each contains any number and combination of "t", "figure", and "section" elements, e.g.,

    <section title="The Middle">
        ...
        <section title="The section Element">
            ...
            <section title="The t Element">...</section>
            <section title="The list Element">...</section>
            <section title="The figure Element">...</section>
            <section title="The xref Element">...</section>
            <section title="The eref Element">...</section>
            <section title="The iref Element">...</section>
        </section>
    </section>

2.3.1.1.  The t Element

The "t" element contains any number and combination of paragraphs, lists, and figures. If a cross-reference is needed to a section, figure, or reference, the "xref" element (The xref Element) is used; similarly, if an external-reference is needed, the "eref" element (The eref Element) is used. Indexing of text is provided by the the "iref" element (The iref Element).

2.3.1.2.  The list Element

The "list" element contains one or more items. Each item is a "t" element, allowing for recursion, e.g.,

    <list style="numbers">
        <t>The first item.</t>
        <t>The second item, which contains two bulleted sub-items:
            <list style="symbols">
                <t>The first sub-item.</t>
                <t>The second sub-item.</t>
            </list>
        </t>
    </list>

The "list" element has an optional attribute, "style", having the value "numbers" (for numeric lists), "symbols" (for bulleted lists), "hanging" (for hanging lists), or, "empty" (for indented text). If a "list" element is nested, the default value is taken from its closest parent; otherwise, the default value is "empty".

When nested within a "hanging list" element, the "t" element has an optional attribute, "hangText" that specifies the text to be inserted, e.g.,

    <list style="hanging">
        <t hangText="full2026:">indicating that the document is in
        full conformance with all the provisions of Section 10 of
        RFC 2026;</t>

        <t hangText="noDerivativeWorks2026:">indicating that the
        document is in full conformance with all the provisions of
        Section 10 of RFC 2026 except that the right to produce
        derivative works is not granted; or,</t>

        <t hangText="none:">indicating that the document is NOT
        offered in accordance with Section 10 of RFC 2026, and
        the author does not provide the IETF with any rights other
        than to publish as an Internet-Draft.</t>
    </list>

2.3.1.3.  The figure Element

The "figure" element groups an optional "preamble" element, an "artwork" element, and an optional "postamble" element together. The "figure" element also has an optional "anchor" attribute that is used for cross-referencing with the "xref" element (The xref Element). There is also an optional "title" attribute that identifies the title of the figure.

The "preamble" and "postamble" elements, if present, are simply text. If a cross-reference is needed to a section, figure, or reference, the "xref" element (The xref Element) is used; similarly, if an external-reference is needed, the "eref" element (The eref Element) is used. Indexing of text is provided by the the "iref" element (The iref Element).

The "artwork" element, which must be present, contains "ASCII artwork". Unlike text contained in the "t", "preamble", or "postamble" elements, both horizontal and vertical whitespace is significant in the "artwork" element.

So, putting it all together, we have, e.g.,

    <figure anchor="figure_example">
        <preamble>So,
        putting it all together, we have, e.g.,</preamble>
        <artwork>
            ascii artwork goes here...

            be sure to use "&lt;" or "&amp;" instead of "<" and "&",
            respectively!
        </artwork>
        <postamble>which is a very simple example.</postamble>
    </figure>

which is a very simple example.

If you have artwork with a lot of "<" characters, then there's an XML trick you can use:

    <figure>
        <preamble>If you have artwork with a lot of "&lt;"
        characters, then there's an XML trick you can
        use:</preamble>
        <artwork><![CDATA[
            ascii artwork goes here...

            just don't use "]]" in your artwork!
        ]]></artwork>
        <postamble>The "&lt;![CDATA[ ... ]]>" construct is called
        a CDATA block -- everything between the innermost brackets
        is left alone by the XML application.</postamble>
    </figure>

The "<![CDATA[ ... ]]>" construct is called a CDATA block -- everything between the innermost brackets is left alone by the XML application.

Because the "figure" element represents a logical grouping of text and artwork, an XML application producing a text version of the document should attempt to keep these elements on the same page. Because RFC 2223 (Postel, J. and J. Reynolds, “Instructions to RFC Authors,” October 1997.) [2] allows no more than 69 characters by 49 lines of content on each page, XML applications should be prepared to prematurely introduce page breaks to allow for better visual grouping.

Finally, the "artwork" element has two optional attributes: "name" and "type". The former is used to suggest a filename to use when storing the content of the "artwork" element, whilst the latter contains a suggestive data-typing for the content.

2.3.1.4.  The xref Element

The "xref" element is used to cross-reference sections, figures, and references. The mandatory "target" attribute is used to link back to the "anchor" attribute of the "section", "figure", and "reference" elements. The value of the "anchor" and "target" attributes should be formatted according to the token syntax in Section 2.1 (XML basics).

If used as an empty element, e.g.,

    according to the token syntax in <xref target="xml_basics" />.

then the XML application inserts an appropriate phrase during processing, such as "Section 2.1" or "<a class="#xml_basics">XML Basics</a>".

If used with content, e.g.,

    conforming to <xref target="refs.RFC2223">RFC 2223</xref>.

then the XML application inserts an appropriate designation during processing, such as "RFC 2223[2]" or "<a class="#refs.RFC2223">RFC 2223</a>". Although the XML application decides what "an appropriate designation" might be, its choice is consistent throughout the processing of the document.

2.3.1.5.  The eref Element

The "eref" element is used to reference external documents. The mandatory "target" attribute is a URI (Berners-Lee, T., Fielding, R., and L. Masinter, “Uniform Resource Identifiers (URI): Generic Syntax,” August 1998.) [4], e.g.,

    <eref target="metalab.unc.edu/xml/">Cafe con Leche</eref>

Note that while the "target" attribute is always present, the "eref" element may be empty, e.g.,

    <eref target="invisible.net/" />

and the XML application inserts an appropriate designation during processing such as "[9]" or "<a class="invisible.net/">invisible.net/</a>".

2.3.1.6.  The iref Element

The "iref" element is used to add information to an index. The mandatory "item" attribute is the primary key the information is stored under, whilst the optional "subitem" attribute is the secondary key, e.g.,

    <iref item="indexing" subitem="how to" />

Finally, note that the "iref" element is always empty -- it never contains any text.

2.3.1.7.  The vspace Element

The "vspace" element, which may occur only inside the "t" element, is used by the author to provide formatting guidance to the XML application. There is an attribute, "blankLines", that indicates the number of blank lines that should be inserted. A physical linebreak is specified by using the default value, "0".

In addition, the "vspace" element can be used to force a new physical paragraph within a list item, e.g.,

    <list style="numbers">
        <t>This is list item.
           <vspace blankLines="1" />
           This is part of the same list item,
           although when displayed, it appears
           as a separate physical paragraph.</t>
    </list>

An XML application producing a text version of the document should exercise care when encountering a value for "blankLines" that causes a pagebreak -- in particular, if a "vspace" element causes a pagebreak, then no further blank lines should be inserted. This allows authors to "force" a pagebreak by using an arbitrarily large value, e.g., "blankLines='100'".

Finally, note that the "vspace" element is always empty -- it never contains any text.

2.4.  Back matter

Finally, the "back" element is used for references and appendices:

        ...
        </middle>
        <back>
            <references>
                <reference ...>
                <reference ...>
            </references>
            <section ...>
            <section ...>
        </back>
    </rfc>

The "back" element consists of an optional "references" element, and, one or more optional "section" elements. The "back" element itself is optional, if your document doesn't have any references or appendices, you don't have to include it.

2.4.1.  The references Element

The "references" element contains the document's bibliography. It contains one or more "reference" elements.

Each "reference" element contains a "front" element and one or more optional "seriesInfo" elements.

We've already discussed the "front" element back in Section 2.2 (Front matter).

The "seriesInfo" element has two attributes, "name" and "value" that identify the document series and series entry, respectively.

The "reference" element has an optional "anchor" attribute that is used for cross-referencing with the "xref" element (The xref Element), e.g.,

    <reference anchor="refs.RFC2200">
        <front>
            <title>Internet Official Protocol Standards</title>
            <author initials="J." surname="Postel"
                    fullname="Jon Postel">
                <organization abbrev="ISI">
                USC/Information Sciences Institute
                </organization>
            </author>

            <date month="June" year="1997" />
        </front>
        <seriesInfo name="RFC" value="2200" />
        <seriesInfo name="STD" value="1" />
    </reference>

The "reference" element also has an optional "target" attribute that is used for external references (c.f., Section 2.3.1.5 (The eref Element)). The XML application, if producing an HTML version of the document will use the "target" attribute accordingly; however, if the "name" attribute of the "seriesInfo" element has the value "RFC", then the XML application should automatically provide an appropriate default for the "target" attribute (e.g., "example.com/rfcs/rfc2200.txt").

2.4.2.  Appendices

To include appendices after the bibliography, simply add more "section" elements. (For an example, look at the example at the beginning of Section 2.4 (Back matter).)

2.4.3.  Copyright Status

The copyright st

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