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Re: [xsl] General rule for designing XPath expressions to return items in document order?


Subject: Re: [xsl] General rule for designing XPath expressions to return items in document order?
From: "Costello, Roger L." <costello@xxxxxxxxx>
Date: Fri, 10 Jan 2014 10:56:09 +0000

David wrote:

	I haven't checked the streaming rules in detail
	but I would expect //head to be streamable.
	(You might not be able to access any of the
	child nodes in a streamable way but for example
	count(//head) ought to be able to count all the
	head in the document in a single pass.

Michael responded:

	That's a fair summary. //head is "consuming"
	(it reads the input stream), and "crawling"
	(it accesses all the nodes in the subtree). When
	you get an expression that is consuming and
	crawling, you are allowed to do "inspection"
	operations on the result, for example count()

But Michael doesn't that contradict section 19.1 of the XSLT 3.0
specification:

	For example <xsl:value-of select="//head"/> will
	still fail the streamability tests, because of the
	possibility that one head element is a child of
	another. This problem can be remedied by
	writing <xsl:value-of select="//head/text()"/>.

/Roger


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