How to find DTD file using DOMBuilder::parseURI()

[Mike Oliver]

I'm having a bit of difficulty finding a way to use
DOMBuilder::parseURI() when the DTD file is not in the
same directory as the XML file.  I've tried calling
DOMBuilder::loadGrammar() immediately previously, even
turning caching on, but it doesn't seem to make any
difference; when I go to parse the XML file, if the
DTD file isn't right there in the same directory, it
chokes.  Any ideas?