Why namespaces?

[Mark Birbeck]

David Carlisle wrote:
> Paul Prescod wrote
> > In XSL you would just use local names. URI-prefixed names are not
useful
> > because you can't mix XHTML with other vocabularies *anyhow*.
> > 
> > If you really did want to use URIs you could do something along the
> > lines of:
> > 
> > <xsl:template match='P[uri()=="$html1" or uri()=="$html2" ...'>
> > 
> > </xsl:template>
>
> No. 
> 
> match='P' matches a P from the currently declared default namespace
> so at most one of the clauses in that or filter could 
> possibly be true.
> You need something like:
> 
> <xsl:template match='html1:P |html2:P | html3:P'>
> 
> </xsl:template>
> 
> You can't just `use local names'. (Of course you could make one of the
> three the default and not use a prefixed form for that one)

Not quite. A template of 'P' would match all elements that have a local
name 'P', regardless of the namespace they came from, *unless* another
template was more precise. For example:

<xsl:template match="P">
	do this most times
</xsl:template>

<xsl:template match="strict:P">
	but do this on others
</xsl:template>

<xsl:template match="xlink:*">
	and do this for anything in one
	particular namespace
</xsl:template>

XSLT uses a scoring mechanism to work out which template should be used
when there is ambiguity.

> It appears that XHTML is defined as an application of XML 1.0 rather
> than XHTML 1.0 + namespaces, so it isn't at all clear why it 
> has to have _any_ namespace allocated.

I think each XML grammar needs its own namespace, since we want to be
able to mix documents within 'documents' all over the shop in manners
that we had never thought of in advance. We therefore need EVERYTHING to
be XML 1.0+namespaces.

Mark

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