xsl] Random Namespaces Declared with XSLT Stylesheet..

>The stylesheet seems to randomly put namespace declarations
>where they're not needed.

I haven't dug into the specific example, but some general thoughts on what
you may be seeing:


"Needed" is determined by sevaral factors.

One is that the prefix is being used in an output element or attribute and
isn't already bound to the correct namespace in that context. In this case,
of course, failing to do so would yield an incorrect result document.

But namespace declarations may also be produced when a namespace node is
copied from the source document or stylesheet to the output (though again,
they may be suppressed if a correct prefix binding is already in scope).
And  when an element is copied into the output document, it's namespace
nodes come with it; see 7.1.1 and 7.5 in the XSLT 1.0 spec. This behavior
is not optional or conditional... and in order to make sure a namespace
node exists in the output document, Xalan (and any other XSLT processor)
has to generate a declaration.


If you want to spend the effort, you can have Xalan output SAX and write
your own logic which attempts to filter out namespace nodes which aren't
being used before routing the SAX stream to a serializer. I don't recommend
doing so. Determining whether a namespace declaration is required by a
subtree would require that you buffer that tree in memory while this is
determined, which would have significant performance impact. The filtering
determination becomes even more expensive if the prefix might be used in
content rather than in a QName -- in an XPath, for example -- since you're
now talking about walking through all the string content
character-by-character.


Or you can avoid copying elements and instead explicitly regenerate them
with <xsl:element/>. But then it then becomes your responsibility to make
sure any namespace nodes that are requried are generated, and XSLT 1.0
doesn't have a clean way of explicitly adding a namespace node. (XSLT 2.0
has a proposal to fix that.)

The usual solution is to shurg and accept that declarations for unused
prefixes are ugly but mostly-harmless.


______________________________________
Joe Kesselman, IBM Next-Generation Web Technologies: XML, XSL and more.
"The world changed profoundly and unpredictably the day Tim Berners Lee
got bitten by a radioactive spider." -- Rafe Culpin, in r.m.filk


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