Hallo Julien,
to process only parts of a html file, you can use the show-body-only
configuration option which you can set to "yes", "no" or
"auto".
For example if you have a file with just this in it:
<a HREF="SOMETHING">LINK</A>
and you run:
tidy --show-body-only auto FILENAME.html
it will fix that snippet and not add any other tags. I think it should work for
Zope as well, as Zope templates are valid xml, IIRC.
Ciao
--
Frank