As per Relevance of the word optional, we have this rfc below:

---

Network Working Group M.
Request for Comments: 2629 Invisible Worlds, Inc
Category: Informational June 1999


Writing I-Ds and RFCs using

Status of this

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

Copyright

Copyright (C) The Internet Society (1999). All Rights Reserved



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





























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RFC 2629 Writing I-Ds and RFCs using XML June 1999


Table of

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 3
2. Using the DTD to Write I-Ds and RFCs . . . . . . . . . . . 4
2.1 XML basics . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 Front matter . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.1 The title Element . . . . . . . . . . . . . . . . . . . . 6
2.2.2 The author Element . . . . . . . . . . . . . . . . . . . . 7
2.2.3 The date Element . . . . . . . . . . . . . . . . . . . . . 8
2.2.4 Meta Data Elements . . . . . . . . . . . . . . . . . . . . 8
2.2.5 The abstract Element . . . . . . . . . . . . . . . . . . . 9
2.2.6 The note Element . . . . . . . . . . . . . . . . . . . . . 9
2.2.7 Status, Copyright Notice, Table of Contents . . . . . . . 9
2.2.7.1 Conformance with RFC 2026 . . . . . . . . . . . . . . . . 9
2.2.8 Everything in the Front . . . . . . . . . . . . . . . . . 10
2.3 The Middle . . . . . . . . . . . . . . . . . . . . . . . . 11
2.3.1 The section Element . . . . . . . . . . . . . . . . . . . 11
2.3.1.1 The t Element . . . . . . . . . . . . . . . . . . . . . . 12
2.3.1.2 The list Element . . . . . . . . . . . . . . . . . . . . . 12
2.3.1.3 The figure Element . . . . . . . . . . . . . . . . . . . . 13
2.3.1.4 The xref Element . . . . . . . . . . . . . . . . . . . . . 15
2.3.1.5 The eref Element . . . . . . . . . . . . . . . . . . . . . 15
2.3.1.6 The iref Element . . . . . . . . . . . . . . . . . . . . . 16
2.3.1.7 The vspace Element . . . . . . . . . . . . . . . . . . . . 16
2.4 Back matter . . . . . . . . . . . . . . . . . . . . . . . 17
2.4.1 The references Element . . . . . . . . . . . . . . . . . . 17
2.4.2 Appendices . . . . . . . . . . . . . . . . . . . . . . . . 18
2.4.3 Copyright Status . . . . . . . . . . . . . . . . . . . . . 18
3. Processing the XML Source File . . . . . . . . . . . . . . 19
3.1 Editing . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.1.1 Checking . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.2 Converting to Text Format . . . . . . . . . . . . . . . . 20
3.3 Converting to HTML Format . . . . . . . . . . . . . . . . 20
3.4 Viewing . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.5 Searching . . . . . . . . . . . . . . . . . . . . . . . . 20
4. Security Considerations . . . . . . . . . . . . . . . . . 21
References . . . . . . . . . . . . . . . . . . . . . . . . 22
Author's Address . . . . . . . . . . . . . . . . . . . . . 22
A. The rfc Element . . . . . . . . . . . . . . . . . . . . . 23
B. The RFC DTD . . . . . . . . . . . . . . . . . . . . . . . 24
C. Acknowledgements . . . . . . . . . . . . . . . . . . . . . 29
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . 31








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RFC 2629 Writing I-Ds and RFCs using XML June 1999


1.

This memo describes how to write a document for the I-D and
series using the Extensible Markup Language [1] (XML). This memo
three goals

1. To describe a simple XML Document Type Definition (DTD) that
powerful enough to handle the simple formatting requirements
RFC-like documents whilst allowing for meaningful markup
descriptive qualities

2. To describe software that processes XML source files, including
tool that produces documents conforming to RFC 2223 [2],
format, and so on

3. To provide the proof-of-concept for the first two goals (
memo was written using this DTD and produced using
software).

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

o allows the traditional production of textual RFC-like
using familiar editors

o requires some, albeit minimal, additions to existing
environments; and

o permits information to be organized, searched, and retrieved
both unstructured and structured mechanisms




















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RFC 2629 Writing I-Ds and RFCs using XML June 1999


2. Using the DTD to Write I-Ds and

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

If you're already familiar with XML, skip to Appendix B to look
the DTD

2.1 XML

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

1. An "element" usually refers to a start tag, an end tag, and
the characters in between, e.g., "text and/or
elements"

2. An "empty element" combines the start tag and the end tag, e.g.,
"". You don't find these in HTML

3. An "attribute" is part of an element. If present, they occur
the start tag, e.g., "". Of course,
can also appear in empty elements, e.g., "".

4. An "entity" is a textual macro that starts with "&". Don't
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
either a letter or an underscore ("_"). Any characters
follow are either letters, numbers, an underscore, or a
(".").

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



...

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

Second, make sure that all elements are properly matched and nested



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A properly matched element that starts with "" is
followed with "". (Empty elements are always matched.)
Elements are properly nested when they don't overlap

For example

...
...
...

is properly nested

However

...
...
...

overlaps, so the elements aren't properly nested

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

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

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



Finally, XML is case sensitive





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RFC 2629 Writing I-Ds and RFCs using XML June 1999


2.2 Front

Immediately following the "" tag is the "front" element