> I've troubles to get document-uri function working in Saxon 8.6,
> even though I had it working in Saxon 8.5.1. 

The implementation of document-uri() in 8.5.1 wasn't conformant, in that it
didn't guarantee that 

doc(document-uri($x)) is $x

would always be true. The spec says that for documents where no such URI is
known, you should return an empty sequence, so that's what Saxon now does. I
agree it would be more helpful to try an assign a document URI that
satisfies the above condition. In the meantime, though, I suspect that the
base-uri() function might be good enough for your needs.

Michael Kay
http://www.saxonica.com/