2008/9/16 David Carlisle <davidc(_at_)nag(_dot_)co(_dot_)uk>:
b) the -or-self part of the // axis is pointless when starting at the root
Actually I think I mislead you there.
two reasons,
firstly //foo always selects the same nodes as
decendant::foo even if used as a relative xpath. Because there is an
implied child axis in the final step.
//self::foo selects the same nodes as /descendant-or-self::foo
secondly you have to be careful about trees whose root node is an
element. If the current node is such a parentless foo element then
descendant::foo will not select the element, descendant-or-self::foo
will select the element and //foo is an error
XPDY0050: The root of the tree containing the context item is not a document
node
<xsl:stylesheet version="2.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform";>
<xsl:variable name="x" as="element()">
<foo a="1">
<foo a="2"/>
<foo a="3"/>
</foo>
</xsl:variable>
<xsl:template name="main">
<xsl:for-each select="$x">
<!--A: <xsl:value-of select="//foo/@a"/>-->
B: <xsl:value-of select="root()//foo/@a"/>
C: <xsl:value-of select="root()//self::foo/@a"/>
<!--D: <xsl:value-of select="/descendant::foo/@a"/>-->
E: <xsl:value-of select="root()/descendant::foo/@a"/>
<!--F: <xsl:value-of select="/descendant-or-self::foo/@a"/>-->
G: <xsl:value-of select="root()/descendant-or-self::foo/@a"/>
</xsl:for-each>
</xsl:template>
</xsl:stylesheet>
B: 2 3
C: 1 2 3
E: 2 3
G: 1 2 3
Nice... had to read that a few times and think about it, especially
calling root() on variable with type element()...
Consider:
<xsl:variable name="x" as="element()+">
<foo/>
<foo/>
</
Calling count($x/root()) returns 2.... which is odd at first, but not
really when each element is both an element and a root node.
Calling count($x[2]/preceding-sibling::*) returns 0, because
effectively the two are separate trees, which helps explain the usual
sibling issues with rootless trees (er, what's the terminology here -
"sequence of element-root nodes"?)
Either way, perhaps it should have read:
b) the -or-self part of the // axis is pointless when starting at a
document node
--
Andrew Welch
http://andrewjwelch.com
Kernow: http://kernowforsaxon.sf.net/
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