[FR] RefTex support for zref-xr

[Gustavo Barros]

Hi All,

RefTeX has support for external documents, as defined by the `xr' 
package, which is really useful when one is using it.

However, there's another package with similar functionality, but 
catering for `zref' references, which is actually a module of `zref' 
itself, named `zref-xr'.  Currently, RefTeX does not support it, and I'd 
like to suggest the inclusion of its support.

The working of `zref-xr' is pretty much identical to that of `xr', and 
the only syntax difference is that the command to import the references 
starts with a "z" (thus `\zexternaldocument'), and it has a starred 
variant.  As far as I can tell, it would suffice to adjust the regexp 
for it in `reftex-parse-from-file' for these minor differences.  Light 
testing suggest it works.

A MWE to illustrate the functionality of the package:

documentA.tex:

#+begin_src latex
\documentclass{article}

\usepackage[user,xr]{zref}

\zexternaldocument[B-]{documentB}

\begin{document}

\section{Section A1}
\zlabel{sec:section-a1}

\zref{B-sec:section-b1}

\end{document}
#+end_src

documentB.tex:

#+begin_src latex
\documentclass{article}

\usepackage[user]{zref}

\usepackage{hyperref}

\begin{document}

\section{Section B1}
\zlabel{sec:section-b1}

\end{document}
#+end_src

Of course, this will result in "No external documents available" if one 
tries to make a reference to `sec:section-b1' from `documentA.tex' with 
RefTeX.  The example is just for the sake of easing things in case 
someone wants to try it out, and to motivate the request.

Side note: If I'm not mistaken, the current regexp would also fail to 
match if the `nocite' argument from `xr-hyper' is in use.

Best regards,
Gustavo.