I've recently been trying to use xref commands with a tags table in a
TeX repository, and many of the results are sub-optimal.  This is a
known issue -- within living memory there have been at least two
discussions related to it on help-gnu-emacs:

https://lists.gnu.org/archive/html/help-gnu-emacs/2018-06/msg00126.html
https://lists.gnu.org/archive/html/help-gnu-emacs/2021-07/msg00436.html

Neither discussion resulted in any code, at least not that I can find,
and the issues mentioned there remain.  For example,
xref-find-definitions on, say, '\mycommand' returns

No definitions found for: mycommand.

(The absence of the escape char in the search string makes the search
fail, as the tag name in the table will be '\mycommand'.)

Similarly, any xref command on 'my:citekey' will only search by default
for the half of the symbol under point, stopping at the colon.

There are many other behaviors that are suboptimal, as well, so in the
end I wrote a new xref backend for TeX buffers (cloning large portions
of the default etags backend), and wondered whether it might be welcome
in GNU Emacs.

A few remarks:

1. The code should work as it stands both in the AUCTeX and the in-tree
modes.  The AUCTeX hooks I've included in the patch are provisional, as
I would want to discuss with them how they would want to handle it,
should the patch be accepted in some form.

2. Along the way I found some issues with how etags parses TeX files,
issues which affect the usefulness of the xref commands, so I've made
changes in etags.c as well.  When running the test suite for etags the
only diffs occurred in the TeX-related sections of the resulting tags
file, and location information in those sections was good.

3. The patch as it stands enables all the changes by default to give
what I judge to be the best out-of-the-box experience, but wiser heads
may well have other ideas.

4. If it looks like the patch will make it into Emacs in some form, I'm
going to need to assign copyright, so I'd appreciate help with getting
that started.

Thanks,

David.