Re: [xsl] Restrictions on XPath expressions in <xsl:key>

Subject: Re: [xsl] Restrictions on XPath expressions in <xsl:key>
From: "G. Ken Holman" <gkholman@xxxxxxxxxxxxxxxxxxxx>
Date: Wed, 19 Dec 2007 16:59:47 -0500
At 2007-12-19 16:39 -0500, Nassar, Anthony wrote:
Does someone know a reason why this won't compile:

<xsl:key name="templates"
ode)/onm:Templates/onm:Template" use="@Name" />

Because match= attributes are restricted to be XPath patterns, not all XPath expressions.

...but this will:

<xsl:template match="onm:Graph">

Because test= is not restricted to only being a pattern.

In other words, why can't an XPath expression in an <xsl:key> element
include parentheses and union operators?

Because patterns are restricted expressions that promote compile-time algorithms for detecting patterns of nodes in the source tree. Not all expressions are like this, so the XPath designers categorized a subset of all XPath expressions, called them patterns, and they are the only ones allowed in a match= attribute.

By the way, what is the order
of precedence between '/' and '|'? I'd understand '\' to have higher
precedence, in which case the latter expression above is actually wrong,
though it's been working for me.

A step separator "/" has higher precedence in the syntax than the expression separator "|", which is why the parentheses are needed to tell a processor that the step is made up of two separate expressions.

Note that in XPath 1.0 the expression separator and parentheses are only allowed in the first step of a multiple-step location path.

I'm using .NET 2.0, so let me know if this is a platform question, in
which case I'll post elsewhere.

It is an XSLT 2.0 question, not a platform-dependent question.

I hope this helps.

. . . . . . . . . . . . . Ken

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