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Network Working Group                                       H. Levkowetz
Internet-Draft                                              Elf Tools AB
Intended status: Informational                        September 28, 2018
Expires: April 1, 2019


 Implementation notes for RFC7991, "The 'xml2rfc' Version 3 Vocabulary"
           draft-levkowetz-xml2rfc-v3-implementation-notes-02

Abstract

   This memo documents issues and observations found while implementing
   RFC 7991.  Individual notes are organised into separate sections,
   depending on their character.

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 https://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 April 1, 2019.

Copyright Notice

   Copyright (c) 2018 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
   (https://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.





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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Fitness for Purpose . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Degraded Table of Contents  . . . . . . . . . . . . . . .   4
     2.2.  Justification of Tables and Artwork . . . . . . . . . . .   5
     2.3.  RFC Publication Date Policy . . . . . . . . . . . . . . .   5
   3.  Schema Issues . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  RFC 7991  . . . . . . . . . . . . . . . . . . . . . . . .   5
       3.1.1.  In Section 2.5.5, "name" Attribute  . . . . . . . . .   5
       3.1.2.  In Section 2.12, <br> . . . . . . . . . . . . . . . .   6
       3.1.3.  In Section 2.20, <dl> . . . . . . . . . . . . . . . .   6
       3.1.4.  New Section 2.20.4, "indent" Attribute  . . . . . . .   7
       3.1.5.  In Section 2.29, <li> . . . . . . . . . . . . . . . .   7
       3.1.6.  In Section 2.32, <name> . . . . . . . . . . . . . . .   8
       3.1.7.  In Section 2.40.2, "quoteTitle" . . . . . . . . . . .   8
       3.1.8.  In Section 2.42, <references> . . . . . . . . . . . .   9
       3.1.9.  In Section 2.45.1, "category" Attribute . . . . . . .   9
       3.1.10. In Section 2.45.3, "docName" Attribute  . . . . . . .   9
       3.1.11. In Section 2.45.7, "number" Attribute . . . . . . . .  10
       3.1.12. In Section 2.53.3 and 2.53.4. . . . . . . . . . . . .  10
       3.1.13. In Section 2.63.2, <ul> "empty" attribute . . . . . .  11
       3.1.14. In Section 3.4.2, "hangIndent" Attribute  . . . . . .  11
       3.1.15. In Appendix C.  Relax NG schema . . . . . . . . . . .  11
       3.1.16. Use of the term "counter".  . . . . . . . . . . . . .  12
     3.2.  RFC 7998  . . . . . . . . . . . . . . . . . . . . . . . .  12
       3.2.1.  In Section 5.2.6, Attribute Default Value Insertion .  12
       3.2.2.  In Section 5.4.6, "pn" Numbering. . . . . . . . . . .  12
   4.  Non-Schema Issues . . . . . . . . . . . . . . . . . . . . . .  13
     4.1.  RFC 7991  . . . . . . . . . . . . . . . . . . . . . . . .  13
       4.1.1.  In Section 2.17, <date> . . . . . . . . . . . . . . .  13
       4.1.2.  In Section 2.47, <seriesInfo> . . . . . . . . . . . .  14
       4.1.3.  In Appendix A.1.1: TLP switch-over date discrepancies  15
       4.1.4.  Index . . . . . . . . . . . . . . . . . . . . . . . .  15
       4.1.5.  Anchors . . . . . . . . . . . . . . . . . . . . . . .  15
       4.1.6.  In Section 2.5.7, "type" Attribute  . . . . . . . . .  16
     4.2.  RFC 7992  . . . . . . . . . . . . . . . . . . . . . . . .  16
       4.2.1.  In Section 8.1.1, Index Contents  . . . . . . . . . .  16
     4.3.  RFC 7994  . . . . . . . . . . . . . . . . . . . . . . . .  17
       4.3.1.  Additional Guidance . . . . . . . . . . . . . . . . .  17
     4.4.  RFC 7998  . . . . . . . . . . . . . . . . . . . . . . . .  17
       4.4.1.  In Section 5.2.3, <date> Insertion  . . . . . . . . .  17
       4.4.2.  In Section 5.2.4, "prepTime" Insertion  . . . . . . .  18
       4.4.3.  In Section 5.2.6, Attribute Default Value Insertion .  18
       4.4.4.  In Section 5.2.7, "toc" Attribute . . . . . . . . . .  19
       4.4.5.  In Section 5.2.8, "removeInRFC" Warning Paragraph . .  19
       4.4.6.  In Section 5.3.1, "month" Attribute . . . . . . . . .  19
       4.4.7.  In Section 5.3.2, ASCII Attribute Processing  . . . .  20



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       4.4.8.  New Section: "keepWithNext" Normalisation . . . . . .  20
       4.4.9.  In Section 5.4.2, <boilerplate> Insertion: Only for
               RFCs? . . . . . . . . . . . . . . . . . . . . . . . .  20
       4.4.10. In Section 5.4.2, <boilerplate> Insertion: Error
               Message . . . . . . . . . . . . . . . . . . . . . . .  21
       4.4.11. In Section 5.4.2.1, Compare <rfc> submissionType and
               <seriesInfo> "stream".  . . . . . . . . . . . . . . .  21
       4.4.12. In Section 5.4.2.2, "Status of this Memo" Insertion .  22
       4.4.13. In Section 5.4.3, <reference> "target" Insertion  . .  22
       4.4.14. In Section 5.4.4, <name> Slugification  . . . . . . .  23
       4.4.15. In Section 5.4.6, "pn" Numbering. . . . . . . . . . .  23
       4.4.16. In Section 5.4.7, <iref> Numbering  . . . . . . . . .  25
       4.4.17. In Section 5.4.8.2, "derivedContent" Insertion
               (without Content) . . . . . . . . . . . . . . . . . .  25
       4.4.18. In Section 5.5.1, <artwork> Processing  . . . . . . .  25
       4.4.19. In Section 5.5.2, <sourcecode> Processing . . . . . .  25
       4.4.20. In Section 5.4.8.2, "derivedContent" Insertion. . . .  26
       4.4.21. In Section 5.4.9, <relref> Processing . . . . . . . .  27
       4.4.22. In Section 5.6.3,  <link> Processing  . . . . . . . .  27
       4.4.23. New Section for Index . . . . . . . . . . . . . . . .  27
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  28
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  28
     6.1.  Informative References  . . . . . . . . . . . . . . . . .  28
     6.2.  URIs  . . . . . . . . . . . . . . . . . . . . . . . . . .  29
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  29

1.  Introduction

   Implementation of tool support for [RFC7991] and related
   specifications has been done during 2017 and 2018, split in the
   following individual parts, all implemented as individual modes of
   the python-based xml2rfc processor [XML2RFC]:

   *  An XML converter from vocabulary version 2 [RFC7749] to version 3
      [RFC7991]

   *  A Normalisation processor, "PrepTool", [RFC7997]

   *  An XML to plain text converter [RFC7994] for the version 3
      vocabulary

   *  An XML to html converter [RFC7992] for the version 3 vocabulary
      (work in progress as of 28 Sep. 2018)

   *  A HTML to PDF converter [RFC7995] for the version 3 vocabulary
      (pending as of 28 Sep. 2018)





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   During the implementation work, a number of issues with the
   specification has been found (this was expected at the outset by all
   parties) and a number of observations has been made about limitations
   of the specification and vocabulary version 3 schema, and also
   limitations in the specification of the work to be done.

   The purpose of this memo is to collect those issues and observations
   in one place.

   When this memo says 'the current version of xml2rfc', it refers to
   the latest release of the xml2rfc processor available from the PyPi
   package repository [1] at the date this document was published, as
   given above.  As of 28 Sep. 2018, this was version 2.10.3.

2.  Fitness for Purpose

   The introduction to [RFC7991] states:

      "This document defines the "xml2rfc" version 3 vocabulary: an XML-
      based language used for writing RFCs and Internet-Drafts.  It is
      heavily derived from the version 2 vocabulary that is also under
      discussion.  This document obsoletes the v2 grammar described in
      RFC 7749."

   However, an unstated assumption seems to have been that the new tools
   and formatters would be used primarily to produce HTML output, in
   order to transition to publication of renderings of RFCs in more
   modern formats than plain-text ASCII.

   This is a reasonable and worthwhile goal, but as a result, the schema
   as specified in [RFC7991] has some drawbacks compared with the
   version 2 vocabulary when used to produce Internet-Drafts in the text
   format common within the IETF (Internet Engineering Task Force) at
   this time.

2.1.  Degraded Table of Contents

   Lack of pagination has little impact on direct online readability,
   but when comparing the output of the new text formatter with the old
   one, one aspect leaps out: Since there is no pagination, the table of
   contents simply lists the section headers to a certain depth, without
   any accompanying page numbers.  This makes a surprising difference in
   how useful the table of contents is in getting an initial feel for
   the document.  The at-a-glance information which lets a reader know
   if this is a document of 10 pages or 100 is simply lacking.

   Recommendation:  Add support for pagination in a future version of
      the text formatter.



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   Implementation:  None in the current version of xml2rfc.

2.2.  Justification of Tables and Artwork

   The version 3 schema deprecates the previously available 'align'
   attribute for artwork and tables, and the PrepTool will remove these
   attributes if used.  This makes a previous feature that was
   appreciated by some authors unavailable.  In the text formatter, the
   effect is simply to make all tables and artwork left-aligned, which
   may not be the most readable and polished output, but for the HTML
   formatter it also potentially removes the option of letting text flow
   around smaller artwork and tables in a controlled way.

   Recommendation:  Make the 'align' attribute for artwork and tables
      available again.

   Implementation:  Implemented but inactive in the current version of
      xml2rfc.  The current text formatter code already has support for
      the 'align' attribute for these elements; but since the attribute
      is stripped away by the PrepTool, the code is never invoked.

2.3.  RFC Publication Date Policy

   The specification [RFC7998] says that an error should be generated if
   a <date> specification is found with missing elements; but the RFC
   Editor publishes documents (except for April 1st RFCs) with only year
   and month, no day of month.  The specification disallows this, and in
   effect makes it impossible for the RFC Editor to publish documents
   according to the current policy regarding publication date format.

   Recommendation:  Revert to to the old behaviour, where the tool in
      RFC mode would issue a date with or without day depending on
      whether the <date> element had a day attribute or not.

   Implementation:  All elements of <date> are required in the current
      version of xml2rfc.

3.  Schema Issues

3.1.  RFC 7991

3.1.1.  In Section 2.5.5, "name" Attribute

      "A filename suitable for the contents (such as for extraction to a
      local file)."

   Given the existing use of "name" on <seriesInfo>, this attribute name
   has a semantic dissonance.



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   Recommendation:  Deprecate "name" for use on <artwork> and
      <sourcecode>, and instead use "file", which for <sourcecode> will
      be explicitly rendered, as established as best current practice
      for YANG modules (see for instance RFC 6087 [RFC6087])

   Implementation:  The current version of xml2rfc uses "name".

3.1.2.  In Section 2.12, <br>

   A number of elements permits a mixed content model (see
   Section "Mixed Content Model"): <li>, <blockquote>, <dd>, <td>, and
   <th>.  However, when using the simpler of the two content schemas,
   two of them (<td> and <th>) permit inline line breaks through the use
   of <br> elements; the others do not.  This seems terribly arbitrary.

   Recommendation:  Remove the <br> element completely.  Alternatively,
      permit it to be used all places that 'text' and non-block elements
      may be used (that is, in inline context).

   Implementation:  The current version of xml2rfc renders <br> as a
      newline in all inline contexts.

3.1.3.  In Section 2.20, <dl>

   The current specification says:

      "The "hanging" attribute defines whether or not the term appears
      on the same line as the definition.  hanging="true" indicates that
      the term is to the left of the definition, while hanging="false"
      indicates that the term will be on a separate line."

   This does not match established typographic terminology.  In
   typographic terminology, "hanging indent" describes the case where
   the indentation of the second and subsequent lines of a paragraph is
   greater than the indentation of the first line.  Whether the
   definition in a definition list starts on the first line or not has
   nothing to do with the presence of hanging indent; our definition
   lists will _always_ have hanging indent.

   The 'hanging' attribute also describes something different from what
   the term has been used to describe in the version 2 vocabulary.  This
   will be confusing to users.

   A more descriptive name for the attribute we're talking about would
   be 'start-definition-on-first-line', but that's unwieldy.  Maybe
   'newline="false"' to start the definition on the first line, or
   something like 'definition-start="first"'?




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   Recommendation:  Change this to a different term that is more
      descriptive and does not use typographically incorrect
      terminology.

   Implementation:  The current version of xml2rfc still uses "hanging".

3.1.4.  New Section 2.20.4, "indent" Attribute

   The deprecation of the "hangIndent" attribute on <list> leaves no
   opportunity to control the size of the hanging indent.  In some
   definition lists, it is desirable to have a wide indentation, in
   order to clearly show the terms, in other cases it is more important
   to allow for a larger text volume than the width of the terms would
   allow.

   Recommendation:  Add an "indent" attribute on <dl> to control the
      size of the hanging indent.

   Implementation:  The current version of xml2rfc does not support the
      attribute, but has all the underlying functions needed to apply
      such an attribute.  Internally, an indentation is calculated based
      on length of the <dt> text and the settings of some of the other
      attributes.

3.1.5.  In Section 2.29, <li>

3.1.5.1.  Unordered lists with arbitrary symbols

   When <li> is used with <ul empty="true">, the rendering is under-
   specified (the specification say 'no label will be shown", but
   doesn't say whether list indentation (leading white-space) should be
   eliminated or not.

   If the intention is to make it possible to render unordered lists
   with arbitrary symbols, chosen on a per-list-item basis, the current
   attributes of <li> are insufficient to indent and line-wrap list
   items properly with <ul empty='true'>.

   It is not possible, for instance, to use <ul> lists to generate XML
   for a table of content, since if the width of the bullet (the section
   number, in this case) is unknown, the proper indentation and line
   wrapping cannot be determined.

   Recommendation:  Add an explicit "bullet" attribute to support this
      use case.






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   Implementation:  None in the current version of xml2rfc, but
      internally bullets are taken a configurable bullet list, so
      accommodating such an attribute would be trivial.

3.1.5.2.  Mixed Content Model

   The mixed content model for <li> --- either text and inline elements
   like sub, sup, bcp14, _or_ <t>, <ul>, <figure> etc, is non-intuitive
   and may be hard for users to keep straight.

   Recommendation:  Consider simplifying the schema by requiring that
      text and inline elements always are placed within a <t> element.

   Implementation:  Not done in the current version of xml2rfc.

   This would apply also to other elements that today have alternative
   content models: <blockquote>, <dd>, <td>, and <th>.

3.1.6.  In Section 2.32, <name>

   So the <name> element can contain text or <tt>, and <tt> can contain
   other markup like <sub> and <sup> etc., but why cannot <name> contain
   <sup> etc.  directly?

   Recommendation:  Change the <name> element schema to permit all
      inline elements that <tt> can contain, in addition to <tt>.

   Implementation:  Not changed in the current version of xml2rfc.
      Implementing this would be a simple matter of changing the v3
      schema; no formatter changes would be needed.

3.1.7.  In Section 2.40.2, "quoteTitle"

   The version two xml2rfc processors already support the attribute
   "quote-title".  The attribute name change introduces an
   incompatibility.  This in particular impacts existing bibxml
   reference files, which should work with both version 2 and 3
   vocabulary documents.

   Recommendation:  Change the attribute name back to the value
      supported by the vocabulary version 2 modes of xml2rfc.

   Implementation:  The current version of xml2rfc converts "quote-
      title" to "quoteTitle" during v2v3 conversion, but this is really
      sub-optimal.






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3.1.8.  In Section 2.42, <references>

   The v3 schema cannot properly model multiple reference subsections
   contained within one numbered section.  The v2 formatter handled this
   by silently inserting a containing section, but with the introduction
   of the preptool, which in theory should produce a master file from
   which various formatters would produce equivalent results, this
   becomes troublesome, as the automatic insertion of a container
   section is specified for the html formatter, in section 9.8. of RFC
   7992, but not for the text formatter.  It would be much better to
   make the prepped xml explicitly show exactly what should be rendered,
   and not rely on formatters silently insert elements.

   Recommendation:  Update the schema to make it possible for
      <references> to contain <references>, and have the prepped xml
      explicitly show both the encapsulating section and the
      subsections.

   Implementation:  Implemented as proposed in the current version of
      xml2rfc.

3.1.9.  In Section 2.45.1, "category" Attribute

   Changing the "category" attribute of <rfc> to a name value in an
   additional <seriesInfo> makes it much harder than it needs to be to
   look it up.  It also makes the semantics of <seriesInfo> less clear.

   Recommendation:  Remove this, and keep the "category" attribute on
      <rfc>

   Implementation:  The "category" attribute on <rfc> has been kept in
      the current version of xml2rfc, but the additional <seriesInfo> is
      also generated during v2v3 conversion.  For purposes of
      determining the category to render, the attribute on <rfc> is the
      one used.

3.1.10.  In Section 2.45.3, "docName" Attribute

   Changing the "docName" attribute of <rfc> to a name value in an
   additional <seriesInfo> makes it much harder than it needs to be to
   look it up.  It also makes the semantics of <seriesInfo> even less
   clear.  See also Section 4.4.22.

   Recommendation:  Remove this, and keep the "docName" attribute on
      <rfc>

   Implementation:  The "docName" attribute on <rfc> has been kept in
      the current version of xml2rfc.



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3.1.11.  In Section 2.45.7, "number" Attribute

   The RFC number attribute in the <rfc> element is used as a switch to
   control whether an RFC or an Internet-Draft is produced.  Moving what
   is effectively an important controlling switch for the operation of
   the formatters from the main element down into what is arguably an
   obscure combination of attribute values on a <seriesInfo> element
   several levels down from the main element feels wrong.

   Recommendation:  Don't deprecate the number attribute on <rfc>, but
      require that the preptool checks that the number attribute matches
      what's in the <seriesInfo> set.  Explicitly mention that the
      presence of the number attribute on <rfc> causes the generation of
      an RFC rather than an Internet-Draft by the formatters.

   Implementation:  In The current version of xml2rfc, the number
      attribute on <rfc> is used to determine whether to produce an RFC
      or Internet-Draft.  If <seriesInfo> elements are found, but no
      <seriesInfo> with name="RFC" and value set to the number is found,
      a warning is given.  If no <seriesInfo> elements are found, the
      appropriate elements, including one giving the RFC number, is
      inserted.

3.1.12.  In Section 2.53.3 and 2.53.4.

3.1.12.1.  Unnecessary limitation on where the "keepWithNext" attribute
           can be used

   Why keepWithNext only on <t>?  It would be very natural to expect to
   be able to say keepWithNext for 2 tables, or 2 figures, or 2 lists?

   Recommendation:  Permit keepWithNext on all elements that can be
      siblings to <t>.

   Implementation:  Not in the current version of xml2rfc.

3.1.12.2.  Violation of KISS and DRY principles

   keepWithNext on one element is equivalent with keepWithPrevious on
   the following element, provided the following element can have a
   keepWithPrevious attribute.  Providing both violates both KISS [KISS]
   and DRY (Don't Repeat Yourself) [DRY].

   Recommendation:  Keep only one of these two attributes, preferably
      keepWithNext.

   Implementation:  Not in the current version of xml2rfc.




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3.1.13.  In Section 2.63.2, <ul> "empty" attribute

   In v2, this results in a list using space as the bullet, thus each
   list entry is indented as with other bullet symbols.  However, this
   leaves no way to get list entries with arbitrary text that are not
   indented, in order to produce lists such as that used in Table of
   Content and Index.

   Furthermore, the specification does not indicate if <ul empty="true">
   should be rendered with space as a bullet, or without any bullet and
   indentation.  A clarification would be good.

   Recommendation:  Specify that in text output, <ul empty="true">
      should be rendered without any bullet and indentation.  In order
      to produce unordered lists that are indented, the "bullet"
      attribute mentioned in Section 3.1.5 with a white-space bullet
      could be used.

   Implementation:  The current version of xml2rfc introduces a new
      attribute "bare" with the possible values "false" | "true" to
      signal this.  The default is "true" (which differs from the
      default v2 implementation).  Using the extra attribute "bare"
      works, but is maybe clumsier than necessary.

3.1.14.  In Section 3.4.2, "hangIndent" Attribute

      "Deprecated.  Use <dl> instead."

   This causes capability loss.  The "hangIndent" attribute did not only
   signal that hanging indent should be used, but also gave the size of
   the indent.  No equivalent control has been provided for the <dl>
   element in the version 3 vocabulary.

   Recommendation:  Provide an attribute "indent" on <dl> as suggested
      in Section 3.1.4.

   Implementation:  Not in the current version of xml2rfc.

3.1.15.  In Appendix C.  Relax NG schema

   The "colspan" attribute is given a default value of "0", this should
   be "1".  "0" is not otherwise defined in the text, and the only
   reasonable interpretation would be to hide the cell (make it occupy
   zero columns).

   The "rowspan" attribute is given a default value of "0", this should
   be "1".  "0" is not otherwise defined in the text, and the only




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   reasonable interpretation would be to hide the cell (make it occupy
   zero rows).

   Recommendation:  Change the default values of "colspan" and "rowspan"
      to 1.

   Implementation:  Done in the current version of xml2rfc.

3.1.16.  Use of the term "counter".

   The classical meaning of this term is a a monotonically increasing
   sequence of integers, globally unique or unique within a context.  In
   this document, it is instead meant to indicate section, table, figure
   numbers, which for sections are not plain counters.

   To make more interesting, in other contexts in the document, the
   notation "-nnn", which also would normally indicate a dash followed
   by digits, i.e., a counter, is also re-interpreted to include section
   numbers; strings of numbers including embedded period signs.  This is
   bad terminology.

   Recommendation:  Instead of "counter", use "number" as the attribute
      value, and explicitly say "Section number, Figure number,
      Table number or ordered list labels" in the description.  Use
      "-n.n" instead of "-nnn".

   Implementation:  Not in the current version of xml2rfc.

3.2.  RFC 7998

3.2.1.  In Section 5.2.6, Attribute Default Value Insertion

   The <seriesInfo> "stream" attribute has a default value of "IETF".
   The effect of setting default values after the XInclude processing is
   to set stream="IETF" on all reference <seriesInfo> which don't have a
   stream set.  This is probably not right.

   Recommendation:  Remove the default value for the "stream" attribute
      from the <seriesInfo> element in the v3 schema.

   Implementation:  The current version of xml2rfc removes the default
      value for the "stream" attribute from the schema.

3.2.2.  In Section 5.4.6, "pn" Numbering.

   The list of elements that are given p- or paragraph tags is severely
   limited, and since the presence of a pn= attribute is required in
   order to make internal <xref> instances work, this limits the



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   elements to which it is possible to reference with html fragment
   identifiers.  Why?
   Why is <dt> and <li> present, but not <ol>, <dl>, <ul>?

   Recommendation:  Permit and provide "pn" numbers of type 'paragraph-
      nnn' for all block-level elements that don't have "pn" numbers
      otherwise specified.

   Implementation:  Not in the current version of xml2rfc, but the
      current version adds p- numbering to <list>, <dl>, <dd>, <ol>,
      <ul>, which all are allowed to have pn= attributes according to
      the schema.

4.  Non-Schema Issues

4.1.  RFC 7991

4.1.1.  In Section 2.17, <date>

4.1.1.1.  Current Date Requirement

      "When the prep tool is used to create Internet-Drafts, it will
      reject a submitted Internet-Draft that has a <date> element in the
      boilerplate for itself that is anything other than today."

   It is not up to the format definition to set policy for acceptance or
   rejection of draft submissions.  The matter is more complex than the
   text assumes, see for instance datatracker issue #2422.  In addition
   to being inappropriate, this text also quietly changes policy from
   +/- 3 days to +/- 0 days, without saying that it updates RFC 4228
   [RFC4228], which is the current specification of permissible dates in
   draft submissions.  Finally, enforcing this would cause _a lot_ of
   grief and problems.

   Recommendation:  Remove the section.

   Implementation:  The current version of xml2rfc does not reject input
      based on the value of <date>, but warns if the date is more than 3
      days from the current date, in accordance with [RFC4228].

4.1.1.2.  Date Specification in References

      "Bibliographic references: In dates in <reference> elements, the
      date information can have prose text for the month or year.  For
      example, vague dates (year="ca. 2000"), date ranges
      (year="2012-2013"), non-specific months (month="Second quarter"),
      and so on are allowed."




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   The text regarding prose text for month and year in bibliographic
   references is not workable.  How should month and year be combined?
   Some bibliographic references may have date text which requires year
   first, others year last, and so on.  Mixing the described fuzziness
   into the otherwise strict year, month, date format makes little sense
   when the result of combining the year, month and date attributes
   cannot be predictably and correctly rendered.

   Recommendation:  Instead of the current specification, permit either
      that the <date> element may have text content, or an alternative
      attribute to be used for rendering if year, month, or day cannot
      be specified exactly.

   Implementation:  The current version of xml2rfc has not implemented
      this part of the specification, and is waiting for a more workable
      solution.

4.1.2.  In Section 2.47, <seriesInfo>

   The possible and forbidden combinations of attributes for this
   element has now become so convoluted that it's really hard to
   understand how to use it correctly.  This needs a serious
   reconsideration.

   The 'name' attribute is mandatory, and only 3 values are permitted:
   "RFC", "Interned-Draft", and "DOI".  But it is also mandatory to set
   the name to "" for a <seriesInfo> with a status attribute.  Hmm...

   So there are 4, not 3 permitted values: "RFC", "Internet-Draft",
   "DOI", and "".

   This means that all reference files which has things like name="ISO",
   name="W3C Recommendation", etc., etc., have become illegal.

   Recommendation:  Do a rewrite of this that does not add new details
      to the already complex <seriesInfo> semantics, and does not make
      non-IETF reference files obsolete, but actually simplifies the
      model and use.

      Limit the <seriesInfo> element to what is actually needed for use
      within <reference/>, and do not add new functionality related to
      the document <front>.  Deprecate any functionality not related to
      usage within <reference/>.

   Implementation:  Mostly not done in the current implementation, but
      see also Section 3.1.9, Section 3.1.11 and Section 3.2.1





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4.1.3.  In Appendix A.1.1: TLP switch-over date discrepancies

   There are discrepancies between the specified switch-over dates in
   the specification, and those given by the Trust statements:

   *  TLP3.0: The specification says 2009-11-01 but the TLP statement
      says effective date 2009-09-12.

   *  TLP4.0: The specification says 2010-04-01 but the TLP statement
      says effective date 2009-12-28.  The dates on which TLP 4 started
      to be use in published RFCs seems to match the stated effective
      date of 2009-12-28, based on a scan of some RFCs around that date.

   RFC 7991 also states this about the pre5378 text: this text appears
   under "Copyright Notice", unless the document was published before
   November 2009, in which case it appears under "Status of This Memo".
   This does not agree at all with what actual RFCs contain; they seem
   to consistently have this text under Copyright Notice.

   Recommendation:  Correct the dates given in the document to indicate
      the official dates, and correct the text on placement of TLP to
      match actual usage.

   Implementation:  The current version of xml2rfc uses the official
      dates during the preptool processing, not the dates given in RFC
      7991.

4.1.4.  Index

   There is no guidance on the structure of an index, if one is to be
   generated by the preptool.

   Recommendation:  Please provide specification.

   Implementation:  The current version of xml2rfc provides the
      generation of index elements in the prepped XML, but makes no
      claim on the generated XML being optimal.

4.1.5.  Anchors

   Section 5.1 of RFC 7992 says in part:

      "The prep tool produces XML with anchor attributes in all elements
      that need them."

   This is rather vital information regarding the content of the prepped
   xml when building a formatter, unfortunately it is not mentioned in
   RFC 7991.



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   Recommendation:  Add this information to the successor of RFC 7991,
      and to the formatter specifications.

4.1.6.  In Section 2.5.7, "type" Attribute

4.1.6.1.  How should a "src" attribute be handled when no "type" is
          given.

   The v3 schema does not require the 'type' attribute on <artwork> to
   have a value, which makes sense when there's no <artwork> 'src'
   attribute to include.  But if there is a 'src' attribute, but no
   value for 'type', how should the 'src' value be handled?

   The easiest and most explicit handling would be to require a 'type'
   value if there is a 'src' attribute; a more doubtful alternative
   would be to use something like the Linux file magic command to try to
   guess at the content type that 'src' points at.

   Recommendation:  Warn if there is a 'src' and no 'type' value, and
      ignore the 'src' in that case.

   Implementation:  The current version of xml2rfc implements this as
      proposed.

4.1.6.2.  Missing information on how to handle various types

      "The RFC Series Editor will maintain a complete list of the
      preferred values on the RFC Editor web site, and that list is
      expected to be updated over time.  Thus, a consumer of v3 XML
      should not cause a failure when it encounters an unexpected type
      or no type is specified.  The table will also indicate which type
      of art can appear in plain-text output (for example, type="svg"
      cannot)."

   The RFC Series Editor has not yet provided such a table.  It is
   definitely desired, in order to be able to deal correctly with plain-
   text output.

4.2.  RFC 7992

4.2.1.  In Section 8.1.1, Index Contents

   The index has an extra <div> enclosing the contents, starting
   directly after <h2>, while sections explicitly does not have a div
   here.  This irregularity seems quite unnecessary, but makes the
   formatter code more complex than need be.  Could we please align the
   two?




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4.3.  RFC 7994

4.3.1.  Additional Guidance

   *  <aside>: Guidance requested on the rendering.  Now rendered with
      an indentation of 9 relative to surrounding text

   *  <blockquote>: Guidance requested on the rendering.  Now rendered
      with an indentation of 3 spaces, pipe(|), two spaces relative to
      surrounding text.

   *  <sub>: Guidance requested.  Now rendered as _(text)

   *  <sup>: Guidance requested.  Now rendered as ^(text)

   *  <tt>: Guidance requested.  Now rendered as "text"

   *  Guidance for <eref> rendering.  In the html formatter, handling of
      <eref> is straightforward and is specified; it simply translates
      to an external link.  In the legacy text formatter, <eref> was
      handled by inserting an extra <references> subsection called
      "URLs", and adding reference entries for the URLs there, while the
      <eref> citation point got a trailing numeric reference number.
      With the preptool output becoming the authoritative published
      document, this difference won't be reflected in the xml.  The two
      formats would be more aligned if the text formatter renders <eref>
      URLs inline.

      Recommendation:  Change the rendering of <eref> in text to render
         the URL inline within parentheses instead of adding the 'URLs'
         reference subsection.

      Implementation:  Implemented in the current version of xml2rfc.

4.4.  RFC 7998

4.4.1.  In Section 5.2.3, <date> Insertion

   Error if any of year, month, day is missing:

   It is an unnecessary and unwanted restriction when not in RFC
   processing mode to given an error for missing date elements.  Missing
   date elements have been permitted because they make it easier for
   draft authors to rev drafts without having to pay attention to the
   date values every time they generate new output.  This requirement
   should apply only to RFC prepping mode, and only in part:





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   In RFC processing mode, this implicitly changes the RFC-Editor policy
   regarding publication dates, which earlier have specified only year
   and month (except for April 1st RFCs).  Is this intentional?

   Recommendation:  Remove this restriction for draft mode, and modify
      it to require only year and month in RFC mode.

   Implementation:  The current version of xml2rfc warns if not all
      three elements are present in RFC mode.  The tool author considers
      even this inappropriate.

      In Internet-Draft mode, the current implementation handles missing
      elements the same way that the v2 formatters do.

4.4.2.  In Section 5.2.4, "prepTime" Insertion

   This is under-specified, given the detailed requirements on the
   <date> attributes.  Should probably be specified as format according
   to [RFC3339], with year, month, day, hour, minute, and second.

   Recommendation:  Specify the format as RFC3339 compliant with
      resolution at least down to a second.

   Implementation:  Implemented as RFC3339 with year, month, and day up
      to version 2.10.3; changed to the proposal above in the next
      release.

4.4.3.  In Section 5.2.6, Attribute Default Value Insertion

   All the default values in 7991 are also expressed in the v3.rnc
   schema.  Remove text indicating otherwise.  And by the way, it was
   very helpful to extract these from the schema programmatically;
   having them specified otherwise would make it much harder to follow a
   changing schema.

   A number of attributes which are deprecated have default values.  The
   current specification will cause those to be inserted, even if they
   have been removed earlier by the v2v3 converter because they are
   deprecated.  This seems inconsistent.

   Recommendation:  Omit deprecated attributes from the default-setting.

   Implementation:  Not in the current version of xml2rfc.








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4.4.4.  In Section 5.2.7, "toc" Attribute

   It's specified that sections with <boilerplate> ancestors should have
   toc="exclude", but this won't then affect <boilerplate> sections
   which are inserted as part of the processing in 5.4.2.  It would make
   more sense to move this processing to after 5.4.2.

   The logic in the second bullet is flawed.  First it says to set
   elements with children with toc="include" to "include", but then it
   says that it is an error if they are set to "exclude".  Either there
   should be a warning, and the toc= attribute should be updated, or
   there should be an error and termination.  Not both.

   Recommendation:  Move 5.2.7 processing to after 5.4.2, or specify
      that a second pass should be done after boilerplate insertion.  If
      a parent to a section with toc="include" has toc="exclude", an
      error should be generated.

   Implementation:  In order to do the actions of 5.2.7 for boilerplate,
      a second pass is made after boilerplate insertion in the current
      version of xml2rfc.  Handling of inconsistent "toc" attribute
      settings is implemented as proposed.

4.4.5.  In Section 5.2.8, "removeInRFC" Warning Paragraph

   This potentially inserts a new <t> element, but after the default
   setting in 5.2.6.

   Recommendation:  Maybe place default setting after all potential
      element insertions have taken place.

   Implementation:  The current version of xml2rfc deals with this by
      adding default-setting of attributes individually on each new
      elements as they are inserted.  This works, but is more complex
      and probably less efficient than doing default-setting once, after
      any new elements have been inserted.

4.4.6.  In Section 5.3.1, "month" Attribute

      "Normalise the values of "month" attributes in all <date> elements
      in <front> elements in <rfc> elements to numeric values."

   Is that 'in' a direct descendant relationship, or any descendant?
   I.e., does this affect <date> elements in included <reference>
   elements?  Unclear.  (RFC7991 is much clearer on this point, but
   that's not an excuse for being unclear here).

   Recommendation:  Clarify the text.



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4.4.7.  In Section 5.3.2, ASCII Attribute Processing

   The uppercasing of 'ascii' in the section <name> is incorrect in this
   case; the attribute name is explicitly 'ascii', not 'ASCII'.  The
   section name should be '"ascii" Attribute Processing'.

   Recommendation:  Change the title 'ASCII Attribute Processing' to
      refer correctly to the "ascii" attribute: '"ascii" Attribute
      Processing'.

      "In every <author> element ..."

   After the earlier XInclude processing, this will include all the
   author elements in the included references, which the document author
   should not normally change in any way.  Was this the intention?

   Recommendation:  Limit it to /rfc/front/author' elements.

   Implementation:  Implemented in the current version of xml2rfc.

   <title> and <postalLine> also has an "ascii" attribute -- is it a
   mistake that they are not mentioned here?  Assuming so, for the
   preptool implementation.

   What about the ascii* attributes on author?  Assuming they should be
   processed the same way.

   Recommendation:  Process all "ascii" attributes in the document
      <front> as specified, and ignore those within <references>

   Implementation:  Implemented as proposed.

4.4.8.  New Section: "keepWithNext" Normalisation

   Recommendation:  The new section should specify normalisation of
      keepWithNext/keepWithPrevious such as to replace all
      keepWithPrevious with an equivalent keepWithNext on the previous
      element, in case the proposal in Section 3.1.12.2 is not accepted.

   Implementation:  Not in the current version of xml2rfc.

4.4.9.  In Section 5.4.2, <boilerplate> Insertion: Only for RFCs?

      "Create a <boilerplate> element if it does not exist.  If there
      are any children of the <boilerplate> element, produce a warning
      that says "Existing boilerplate being removed.  Other tools,
      specifically the draft submission tool, will treat this condition
      as an error" and remove the existing children."



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   Should this be done in both I-D mode and RFC mode?  The trouble is
   that the following subsections only describes the boilerplate
   relevant to an RFC; there's additional boilerplate that is needed for
   drafts.  I don't think it's reasonable to have a draft with only
   parts of the boilerplate contained in a boilerplate section.

   Recommendation:  The boilerplate-element insertion parts of 5.4.2
      should be done in both RFC and draft mode, with the appropriate
      boilerplate for each case.  For consistency, either add text to
      describe the appropriate boilerplate for drafts, or remove the
      sections specific to RFC boilerplate.

   Implementation:  The current version of xml2rfc inserts boilerplate
      for both drafts and RFCs, as appropriate.

4.4.10.  In Section 5.4.2, <boilerplate> Insertion: Error Message

   This section also specifies an error message to be used verbatim; the
   troublesome thing is that it's not clear what it means.  The message
   is: "Existing boilerplate being removed.  Other tools, specifically
   the draft submission tool, will treat this condition as an error".
   What is it that the draft submission tool is going to treat as an
   error?  The presence of boilerplate?  Why?  The removal of
   boilerplate?  How is that related to draft submission?  This is very
   jumbled.

   Recommendation:  If existing boilerplate is found, issue a warning
      and replace it.

      For other tools, suggest that if boilerplate is present during
      draft submission, it should be checked for validity.  This is
      already a function of idnits, so does not constitute anything new,
      but is decidedly better than having the submission tool actually
      reach into the submitted document and change it.

   Implementation:  In the current version of xml2rfc this is
      implemented as proposed, with the following warning if existing
      boilerplate is found: "Expected no <boilerplate> element, but
      found one.  Replacing the content with new boilerplate."

4.4.11.  In Section 5.4.2.1, Compare <rfc> submissionType and
         <seriesInfo> "stream".

   This comes too late.  It is specified that if either is missing, it
   should be added.  But the default attribute setting earlier has set
   stream="IETF" on all <seriesInfo> elements that didn't have it.  If a
   document is read without submissionType, and stream set correctly to
   something else than "IETF" on one of the <seriesInfo> elements, then



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   the default-setting will have created a conflict which cannot be
   resolved purely from the document at this point.

   Furthermore, it doesn't seem like a good fit to have tag attributes
   that all have to be set to the same value.  This is not DRY, and
   unnecessarily introduces the possibility of conflict, as a result of
   multiple <seriesInfo> elements being permitted (Relevant to the v3
   schema, not the preptool).

   Recommendation:  Remove the default value for stream, and make it
      subordinate to submissionType.

   Implementation:  The current version of xml2rfc implements the
      specification as written, and produces errors (which lead to not
      producing an output document) on inconsistencies.  This does not
      feel user-friendly.

4.4.12.  In Section 5.4.2.2, "Status of this Memo" Insertion

   It specifies that one should consider both submissionType and
   <seriesInfo> stream value; but those have just been set equal in
   5.4.2.1.

   Recommendation:  Remove <seriesInfo> from consideration here.  In
      order to produce a correct "Status of this Memo" text, "category",
      "consensus", and "submissionType" must be considered, and all
      three are present as attributes on <rfc>.  Keep it that way.

   Implementation:  The current version of xml2rfc looks at
      "submissionType", "category", and "consensus" on the <rfc>
      element.

4.4.13.  In Section 5.4.3, <reference> "target" Insertion

      "Insert "target" attributes for RFC, DOI, and Internet-Draft
      references that lack them."

   It is indicated that the rfc-editor will provide the URL patterns.
   What are they?

   In the formatter, the order of <seriesInfo> determines the rendering
   order.  The insertion should probably be done in the desired
   rendering order.

   Recommendation:  In addition to providing the appropriate URL
      patterns, specify the order in which the <seriesInfo> elements
      should occur, for instance: 'BCP', 'RFC', 'DOI'.




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   Implementation:  The current version of xml2rfc inserts the
      appropriate <seriesInfo> elements, and after insertion sorts them
      in the order 'BCP', 'RFC', 'DOI', followed by others.

4.4.14.  In Section 5.4.4, <name> Slugification

   The 'n-' prefix for slugs is unnecessarily opaque.

   Recommendation:  Use slugs with prefix "name-" rather than "n-", to
      be more self-documenting.

   Implementation:  Implemented as proposed in the current version of
      xml2rfc.

   Should the slugs be unique?  Assuming yes, but guidance would be
   good.  The current version of xml2rfc enforces unique slugs, with the
   following algorithm:

   *  remove non-ascii letters

   *  replace-non-letters with dash, compacting multiple dashes to one

   *  reduce length to 32, but insure uniqueness by increasing length or
      adding numerical suffixes, up to length 40 with suffixes numbered
      2 to 99.

   Recommendation:  Do slugification and uniqueness enforcement as
      described above.

   Implementation:  As described above.

4.4.15.  In Section 5.4.6, "pn" Numbering.

   What does 'pn' mean?  Cryptic is never good when humans have to deal
   with it.  At least explain as "part number" in text.  Possibly even
   change pn="" to part="".

   <back><section> is not mentioned.  Assuming numbering as section-
   appendix.1.2

   <iref> elements are not mentioned (but covered in 7991).  Should be
   listed in 7998.

   The numbering scheme is inconsistent between notes/boilerplate and
   other sections, in that if attempting to split a pn on dashes (which
   external tools might want to do) the boilerplate/note sections
   contain an additional dash.




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   Recommendation:  Change that dash to a dot, for better consistency
      with other sections.  This also makes the <t> part numbers less
      confusing: "section-boilerplate.1-1" instead of "section-
      boilerplate-1-1"

   Implementation:  Implemented as proposed in the current version of
      xml2rfc.

4.4.15.1.  RFC format anchors / fragment identifiers

   The anchor prefixes described unnecessarily break with existing links
   to document sections.  Wikipedia has (2018-02-19) about 84 000 pages
   that link to RFCs; with most pages having multiple links.  A small
   manual sampling indicates that about 1 link in 10 has a #section-
   fragment identifier.  All of these will break if the new tools are
   used to generated content linked from these pages.

   How much larger than Wikipedia is the whole of the internet, in terms
   of links to RFCs?  Hard to tell (though searching for 'rfc' on Google
   indicates 'about 10 000 000 results).  In any case, we are talking
   about breaking a substantial number of links using fragment
   identifiers of the format #section- and #appendix- if the new tools
   are used to replace the old html content that sites currently point
   to.

   Recommendation:  update rfc7998 preptool to use these prefixes,
      instead:

      -  "section-xxx"

      -  "figure-xxx"

      -  "table-xxx"

      -  "appendix-xxx"

      -  "index-xxx"

      -  "para-xxx"

      -  "name-xxx"

   Implementation:  Implemented as above in the current version of
      xml2rfc.







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4.4.16.  In Section 5.4.7, <iref> Numbering

   Numbering of <iref> talks about setting the 'pn' attribute.  Mixed
   into this is a mention of 'irefid', which isn't a valid attribute.
   The current implementation assumes that 'pn' is meant.

   The item and sub-item text is not constrained to slug format; in
   order to deliver useful pn values, slugification should be done.  On
   the other hand, the explicit prescription of how to ensure uniqueness
   clashes with the total lack of uniqueness attention under 5.4.4.

   Recommendation:  Require slugification for pn-numbering of items and
      sub-items, but remove the details of how to ensure uniqueness.
      Correct the mention of 'irefid' to say 'pn', if that was intended.

   Implementation:  Slugification is done, and uniqueness is enforced
      with an algorithm that limits slug length and tries to keep slugs
      readable.  If there are more than 99 slugs that would collide if
      no uniqueness processing was done, an error is generated.

4.4.17.  In Section 5.4.8.2, "derivedContent" Insertion (without
         Content)

   There's a formatting mistake:

   The last sentence of the last bullet ("Issue a warning...") should
   not be part of the bullet, but a separate final paragraph for the
   Section.

4.4.18.  In Section 5.5.1, <artwork> Processing

   RFC791 specifies that the <artwork> content is a fallback if there is
   external <svg> content, but 7998 says to drop the fallback and insert
   the external <svg>.  This deletes information, and makes the fallback
   unavailable.  This needs a better handling.

   Recommendation:  If there is fallback content, convert the external
      URL content to a "data:" URL for the src.  This pulls the external
      content in and makes it immutable, but retains the fallback text.

   Implementation:  Implemented as proposed in the current version of
      xml2rfc.

4.4.19.  In Section 5.5.2, <sourcecode> Processing

   List item 4 says:





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      "fill the content of the <sourcecode> element with the resolved
      XML from the URI in the "src" attribute"

   However, we have no particular reason to assume that the content of
   the "src" URL is XML.  Quite to the contrary, it would be a very
   natural and common use case that the external content is a source
   code file.

   Recommendation:  The URI should not be assumed to resolve to xml, but
      instead treated like CDATA.

   Implementation:  Implemented as proposed in the current version of
      xml2rfc.

4.4.20.  In Section 5.4.8.2, "derivedContent" Insertion.

   It is not clear from the description if the derived content text
   should contain square brackets when an <xref> would be rendered with
   square brackets in current output formats.

   It is not clear if the derived content should include the 'Figure',
   or 'Table' label when pointing to such objects.  When rendering such
   a reference in the current output formats, the generated text would
   include the label, but the current text seems to lean towards not
   making this part of the derived content, which would cause
   incompatibility with the output of v2 formatters.

   The purpose of this is insufficiently explained.  If the intention is
   to use this when generating derived formats, there are problems: If,
   for instance, the derived format with a <reference> target is set to
   'RFC1234', the text inserted in a derived format should have
   surrounding square brackets; but if the target is a section, it
   should not.  If on the other hand the derived format includes the
   square brackets when appropriate, the link in a derived format with
   internal link capability will use the whole of the bracketed string,
   rather than the more appropriate text within the brackets.

   Recommendation:  The whole "derivedContent" handling and
      specification needs a thorough rework, with specification of the
      intended use of the attribute by formatters.  Possibly the whole
      "derivedContent" concept should be scrapped, and the rendering
      left for the formatter, depending on the characteristics of the
      output format.

   Implementation:  The current version of xml2rfc works around this
      issue by using different formatter code for different cases, which
      is not good from the viewpoint of using the prepped XML as the
      archival format, but at least produces reasonable output.



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4.4.21.  In Section 5.4.9, <relref> Processing

   Why doesn't <relref> have the same format options as <xref>?  Surely
   they must be just as relevant here.  But more importantly, <relref>
   overlaps <xref> so much that it would be better to just add section,
   relative, and displayFormat to <xref>.  Maybe change displayFormat to
   the earlier proposed 'sectionFormat'.

   Recommendation:  Deprecate <relref>, and fold the functionality into
      <xref>.

   Implementation:  The <relref> functionality has been folded into
      <xref>, but relref support not yet removed.

4.4.22.  In Section 5.6.3, <link> Processing

   Bullet 4.: Bad grammar: s/RFC the form/RFC, in the form/

   Bullet 4.: Hmm.  The <link rel="convertedFrom" href="draft-...">
   should ideally be created automatically, but there is no clear path
   of how to do that.

   Recommendation:  Require docName to be set to the draft name, and use
      that to create this link.  This also implies that "docName" not be
      deprecated (see Section 3.1.10).

   Implementation:  Implemented as proposed in the current version of
      xml2rfc.

4.4.23.  New Section for Index

   RFC7998 does not say a word about inserting xml for the index, if one
   is requested, but it seems counter-intuitive not to produce xml for
   the index as part of the preptool processing, given all the other
   prepping that's being done.  What's more, in Section 2.27 of RFC 7991
   there's this text:

      "When the prep tool is creating index content, it collects the
      items in a case-sensitive fashion for both the item and sub-item
      level."

   Recommendation:  Insert the XML necessary to render the index into
      the prepped XML.

   Implementation:  Implemented as proposed in the current version of
      xml2rfc.





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5.  Security Considerations

   This document does not introduce any security considerations on its
   own.

6.  References

6.1.  Informative References

   [DRY]      Wikipedia, "Don't repeat yourself", 2018,
              <https://en.wikipedia.org/wiki/Don%27t_repeat_yourself>.

   [KISS]     Wikipedia, "KISS Principle", 2018,
              <https://en.wikipedia.org/wiki/KISS_principle>.

   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
              <https://www.rfc-editor.org/info/rfc3339>.

   [RFC4228]  Rousskov, A., "Requirements for an IETF Draft Submission
              Toolset", RFC 4228, DOI 10.17487/RFC4228, December 2005,
              <https://www.rfc-editor.org/info/rfc4228>.

   [RFC6087]  Bierman, A., "Guidelines for Authors and Reviewers of YANG
              Data Model Documents", RFC 6087, DOI 10.17487/RFC6087,
              January 2011, <https://www.rfc-editor.org/info/rfc6087>.

   [RFC7749]  Reschke, J., "The "xml2rfc" Version 2 Vocabulary",
              RFC 7749, DOI 10.17487/RFC7749, February 2016,
              <https://www.rfc-editor.org/info/rfc7749>.

   [RFC7991]  Hoffman, P., "The "xml2rfc" Version 3 Vocabulary",
              RFC 7991, DOI 10.17487/RFC7991, December 2016,
              <https://www.rfc-editor.org/info/rfc7991>.

   [RFC7992]  Hildebrand, J., Ed. and P. Hoffman, "HTML Format for
              RFCs", RFC 7992, DOI 10.17487/RFC7992, December 2016,
              <https://www.rfc-editor.org/info/rfc7992>.

   [RFC7993]  Flanagan, H., "Cascading Style Sheets (CSS) Requirements
              for RFCs", RFC 7993, DOI 10.17487/RFC7993, December 2016,
              <https://www.rfc-editor.org/info/rfc7993>.

   [RFC7994]  Flanagan, H., "Requirements for Plain-Text RFCs",
              RFC 7994, DOI 10.17487/RFC7994, December 2016,
              <https://www.rfc-editor.org/info/rfc7994>.





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   [RFC7995]  Hansen, T., Ed., Masinter, L., and M. Hardy, "PDF Format
              for RFCs", RFC 7995, DOI 10.17487/RFC7995, December 2016,
              <https://www.rfc-editor.org/info/rfc7995>.

   [RFC7996]  Brownlee, N., "SVG Drawings for RFCs: SVG 1.2 RFC",
              RFC 7996, DOI 10.17487/RFC7996, December 2016,
              <https://www.rfc-editor.org/info/rfc7996>.

   [RFC7997]  Flanagan, H., Ed., "The Use of Non-ASCII Characters in
              RFCs", RFC 7997, DOI 10.17487/RFC7997, December 2016,
              <https://www.rfc-editor.org/info/rfc7997>.

   [RFC7998]  Hoffman, P. and J. Hildebrand, ""xml2rfc" Version 3
              Preparation Tool Description", RFC 7998,
              DOI 10.17487/RFC7998, December 2016,
              <https://www.rfc-editor.org/info/rfc7998>.

   [XML2RFC]  Levkowetz, H., "xml2rfc", 2018,
              <https://pypi.org/pypi/xml2rfc>.

6.2.  URIs

   [1] https://pypi.org/pypi/xml2rfc

Author's Address

   Henrik Levkowetz
   Elf Tools AB
   Ollonstigen 8
   Sweden

   Email: henrik@levkowetz.com



















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