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From: http://sources.redhat.com/ml/xsl-list/2002-04/msg01308.html > > I need to quickly find the matching node to the current node > > which is in a parallel branch with identical structure to the > > branch I'm operating in. It seems like this should be really > > simple, but the only solution I can come up with is > > a recursive template to assemble the name of the path from > > the branch tag down, and then compare that against the result > > from the same template for each node in the second tree. The > > trees may be of arbitrary depth. Any other ideas? > One XPath expression that returns the required corresponding node is: $br2//node() [count(preceding::node()) - $br2PrecIndex = $thisRelPrecIndex and count(ancestor::node()) - $br2AncIndex = $thisRelAncIndex ~ where there are the following variable definitions: <xsl:variable name="br1" select="/*/branch1"/> <xsl:variable name="br2" select="/*/branch2"/> <xsl:variable name="thisPrecIndex" select="count(preceding::node())"/> <xsl:variable name="thisAncIndex" select="count(ancestor::node())"/> <xsl:variable name="br1PrecIndex" select="count($br1/preceding::node())"/> <xsl:variable name="br1AncIndex" select="count($br1/ancestor::node())"/> <xsl:variable name="br2PrecIndex" select="count($br2/preceding::node())"/> <xsl:variable name="br2AncIndex" select="count($br2/ancestor::node())"/> <xsl:variable name="thisRelPrecIndex" select="$thisPrecIndex - $br1PrecIndex"/> <xsl:variable name="thisRelAncIndex" select="$thisAncIndex - $br1AncIndex"/> This might seem a little bit complicated, however the idea is quite simple. Every node can be identified in a two-dimensional coordinate system, in which the first axis is the "preceding" axis, and the second axis is the "ancestor" axis (as we know, these two axes are non-overlapping). That is, the pair: (count(preceding::node()), count(ancestor::node())) uniquely identifies any node. The above is an absolute coordinate system (relative to the root node). We can express the pair of coordinates of a node relative to some ancestor (in our case "branch1"). Then the corresponding node in the subtree rooted by "branch2" must have the same pair of coordinates, relative to "branch2". This simple relationship is expressed in the first XPath expression in this message. Cheers, Dimitre Novatchev.