[xml] setting URL for xmlRelaxNGParserCtxt?

[Martijn Faassen <faassen infrae com>]

Hi there,

In my lxml Python binding for libxml2, I was using the following 
approach to construct a Relax NG schemas:

xmlDocPtr* doc = ...
parser_ctxt = xmlRelaxNGNewDocParserCtxt(doc)

unfortunately, this got me into trouble with Relax NG schemas that use 
the 'include' statement. They try to load the files to be included, but 
have no idea where to look, as this information is lost.

Glancing through the source, it seems like the only way to make the 
'include' statement work is to use xmlRelaxNGNewParserCtxt, which takes 
a URL.

Would it be useful to have a way to supply this URL to an existing 
xmlRelaxNGParserCtxtPtr? Something like:

void xmlRelaxNGSetURL(xmlRelaxNGNParserCtxtPtr* ctxt, const char* URL)

Even more powerful, though decidedly more tricky, would be a way to hook 
into the lookup process itself. If my XML is sitting in an object 
database for instance, the current approach would fail, unless I expose 
all relevant XML objects under a URL and refer to that.

I imagine the same issues come up when using XSLT that tries to include 
or import external stylesheets.

Regards,

Martijn