Structure
Note that the subsections of the main sections "Elements" and "Elements from
v2 That Have Been Deprecated" of draft-iab-rfc7991bis.xml are auto-generated
based on:
1) xml2rfcv3.rng, and
2) draft-iab-rfc7991bis.xml itself.
To change the (RNG) *grammar*, edit xml2rfcv3.rng and run "make":
xml2rfcv3-spec.xml: xml2rfcv3.rng rng2xml2rfc.xslt
        $(XSLT) $< rng2xml2rfc.xslt voc=v3 specsrc=draft-iab-rfc7991bis.xml > $@
xml2rfcv3-spec-deprecated.xml: xml2rfcv3.rng rng2xml2rfc.xslt
        $(XSLT) $< rng2xml2rfc.xslt specsrc=draft-iab-rfc7991bis.xml deprecated=yes > $@
This will generate xml2rfcv3-spec.xml and xml2rfcv3-spec-deprecated.xml, based
on the grammar and the prose already present in draft-iab-rfc7991bis.xml.
Example source for <workgroup>:
--- snip ---
<!--workgroup-->
<section xmlns:x="https://purl.org/net/xml2rfc/ext" anchor="element.workgroup">
   <name>
      <tt>&lt;workgroup&gt;</tt>
   </name>
   <x:anchor-alias value="workgroup"/>
   <iref item="Elements" subitem="workgroup" primary="carview.php?tsp=true"/>
   <iref item="workgroup element" primary="carview.php?tsp=true"/>
   <t>
      This element is used to specify the Working Group (IETF) or Research Group (IRTF) from which the document originates,
      if any. The recommended format is the official name of the Working Group
      (with some capitalization).
   </t>
   <t>
      In Internet-Drafts, this is used in the upper left corner of the boilerplate,
      replacing the "Network Working Group" string. Formatting software can
      append the words "Working Group" or "Research Group", depending on
      the "submissionType" property of the &lt;<x:ref>rfc</x:ref>&gt; element
      (<xref target="element.rfc.attribute.submissionType"/>).
   </t>
   <t><!--AG-->This element appears as a child element of &lt;<x:ref>front</x:ref>&gt; (<xref target="element.front"/>).</t>
   <t anchor="element.workgroup.contents"><!--AG-->
      <xref format="none" target="grammar.workgroup">Content model</xref>: only text content.</t>
</section>
--- snip ---
Within this section, <t> elements can be added to the element and attribute
descriptions and are supposed to round-trip through the re-generation
process.
xml2rfcv3-spec.xml and xml2rfcv3-spec-deprecated.xml are re-inserted into the
source file using refresh-inclusions.sh (documented at 
<https://greenbytes.de/tech/webdav/rfc2629xslt/rfc2629xslt.html#refreshing.inclusions>).
Note that this approach was chosen so that the source file remains
self-contained.
Building
Building the spec requires:
1) java
2) xml2rfc
3) Saxon10he (<https://mvnrepository.com/artifact/net.sf.saxon/Saxon-HE/10.2>)
4) Trang (checked in)