What IS a valid URI Reference?

[David Hunter <david.hunter@mobileq.com>]

[I couldn't find it, but if this is an issue that has already been covered,
please point me to the proper posts in the archives, and I'll research this
further offline.]

The namespaces rec says that namespaces are identified by a URI reference,
and points to RFC2396, but I'm wondering:

a)  What should a namespace-aware XML parser do if it encounters a namespace
identifier which is not a valid URI reference?

b)  Is it even possible for the XML parser to tell if a string is a valid
URI Reference?  From some posts I waded through in the archives, it seems
that it may not be cut and dried, when a string doesn't fit with this RFC.

For example, MSXML accepts the following XML document with no qualms:

<blah xmlns="@+_)(*^%%%{}"/>

(and I think Xerces does as well, although my Java skills are weak, and I
just might not be capturing errors properly.)

Is "@+_)(*^%%%{}" really a valid URI Reference?  (Section 2.2 of RFC2396
seems to indicate that at the very least the "@" and "+" characters would
have to be escaped...)  And if not, are there parsers which would reject it?

Any insights that are provided will be useful.

David Hunter
Senior Architect
MobileQ
david.hunter@mobileq.com
http://www.mobileq.com