2.2.13 [W3C-XSLT] Section 12.1, Multiple Source Documents
The specification states:
If there is an error retrieving the resource [an XML document specified by URI reference], then the XSLT processor may signal an error; if it does not signal an error, it must recover by returning an empty node-set. One possible kind of retrieval error is that the XSLT processor does not support the URI scheme used by the URI. An XSLT processor is not required to support any particular URI schemes. The documentation for an XSLT processor should specify which URI schemes the XSLT processor supports.
MSXML3 and MSXML6
If there is an error retrieving the resource, the XSLT processor signals an error and does not return an empty node set.
The XSLT processor supports the following URI schemes:
File Transfer Protocol
Hypertext Transfer Protocol
Electronic mail address
Note In response to a
mailto request, the XSLT processor first requests privilege to display a New Mail window using the default mail sender. The window is displayed only if privilege is granted.