Proper way to specify UNC path in XML catalog

Hello,

I've recently run into trouble trying to specify a UNC pathname in an
XML catalog. The pathname has the form:

\\server\path\

For xsltproc, the following seems to work:

file://///server/path/   (5 forward slashes)

and for Saxon/Xerces this works:

file:////server/path/   (4 forward slashes)

Is there an "official" way to specify an UNC pathname for XML
catalogs? And maybe even something that works with both xsltproc and
Saxon/Xerces?

Thanks,
Ken