I could quote Frank's response to Sebastian, but I won't.
The question lingers, however, as to whether we view xml as off topic
here. On the one hand, xmltex is something that runs through LaTeX,
and, on the other hand, if xml is a presence, it changes the package
writing scene inasmuch as some of the things that people get from
packages can be provided (sometimes better) before regular LaTeX
I know that there were lots of bad early experiences that some had
with sgml. It need not be that way.