The XSLT 1.0 spec contains a number of statements about what is supposed to
happen:

The xsl:include element has an href attribute whose value is a URI reference
identifying the stylesheet to be included. A relative URI is resolved
relative to the base URI of the xsl:include element (see [3.2 Base URI])...
The resource located by the href attribute value is parsed as an XML
document, and the children of the xsl:stylesheet element in this document
replace the xsl:include element in the including document.

You have to read all these statements with an implicit "If possible then X
happens, otherwise an error is signaled".

> -----Original Message-----
> From: Bob Foster [mailto:bob@xxxxxxxxxx] 
> Sent: 24 April 2004 15:52
> To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
> Subject: Re:  Is it an error if can't resolve uri-reference?
> 
> Michael Kay wrote:
> >>Is it an error if, when processing an include or import element, a 
> >>stylesheet processor can't resolve the href uri-reference?
> > 
> > 
> > Yes, it's an error.
> > 
> >>The 1.0 spec doesn't say that it is. Or did I miss it?
> > 
> > 
> > The 1.0 spec doesn't try to list all the things that can go wrong.
> 
> Is there any document that does? How is an implementor supposed to 
> decide whether to treat this as an error or ignore it?
> 
> I know this is all water under the bridge for you, but now 
> you've got me 
> wondering what other errors (not implied by syntax or 
> described by other 
> specs) aren't called out in the spec?
> 
> Bob Foster