First, am I right that if I use an "as" attribute of element() or
node() I am passing a reference to the original element or node, and
thus that this is an efficient operation?
In the examples below you are passing a reference. If you used xsl:copy-of
rather that xsl:sequence you would be creating a copy.
The effect of using "as" on performance may be positive or negative. It may
cause the system to do run-time checks that would otherwise not be
performed. On the other hand, it gives the system compile-time information
that may be useful to perform optimizations. I would use it as widely as
possible because it speeds the development cycle and catches bugs more
efficiently, and not worry too much about any effect on performance.
Related, am I correct that these below are equivalent from a
processing
standpoint?
<xsl:variable name="foo" select="bar" as="element()"/>
<xsl:variable name="foo" as="element()">
<xsl:sequence select="bar"/>
</xsl:variable>
Yes.
Finally, in general, under what conditions should one use tunnel
parameters? I do a lot of parameter passing in my
stylesheets, though
the content of those parameters is typically fixed.
Use them if A calls E via B, C, and D, and you want to get information from
A to E without cluttering the code of templates B, C, and D. The most likely
use-case for this is if you are reusing existing templates B, C, and D and
want to reuse them unchanged.
Michael Kay
http://www.saxonica.com/
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