nXML mode maintenance and enhancement

["N. Raghavendra" <nyraghu27132@gmail.com>]

I would like to help with the maintenance and enhancement of nXML mode.
Here are some things which may be considered:

1. Make indentation in nXML mode compatible with that in the official
   SGML mode, and in the unofficial PSGML mode; the latter indentation
   styles are arguably more natural, and followed by projects like the
   FreeBSD Documentation Project.  I had stumbled across this problem
   recently, as in
   https://lists.gnu.org/archive/html/help-gnu-emacs/2018-05/msg00009.html

2. Addition of features in PSGML mode, e.g,

   a) Information about the schema: analogues of
      `sgml-describe-element-type', `sgml-list-elements', etc.

   b) Support for processing instructions such as, e.g.,

      <?PSGML ELEMENT foo nofill=t>

      which specify that a `foo' element should not be disturbed when
      filling a region; this is useful if one wants to fill a buffer
      containing verbatim elements such as program listings.

   c) Provision of more editing commands analogous to `sgml-tag-region',
      `sgml-auto-insert-required-elements', etc.

3. Support for XInclude.

4. Provision of a facility similar to RefTeX for manipulating
   cross-references in a modular document.

5. Analogues of `LaTeX-fill-region' and friends from AUCTeX.

6. More documentation.

I would like advice on how to proceed.

Thanks,
Raghu.

--
N. Raghavendra <raghu@hri.res.in>, http://www.retrotexts.net/
Harish-Chandra Research Institute, http://www.hri.res.in/