XSLT: Copying node data to another node by matching attribute value, Efficiently? - xslt

Question

I coded the XSLT to copy one node data to another by validating the attribute value, I got the desired output but I'm curious to know whether there is an efficient way to do this or if this is the only way to do it. [I'm not an XSLT expert] Can someone help !!!
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https://xsltfiddle.liberty-development.net/pNvtBH2/3
Actual XML:
<?xml version="1.0" encoding="utf-8" ?>
<section>
<p>note 1 : 1</p>
<p>note 2 : 2</p>
<p>note 3 : 3</p>
<note id="test1">hello one</note>
<note id="test2">hello two</note>
<note id="test3">hello <i>three</i></note>
<note id="test4">hello <i>four</i></note>
</section>
Output:
<?xml version="1.0" encoding="UTF-8"?><section>
<p>note 1 : <a>hello one</a></p>
<p>note 2 : <a>hello two</a></p>
<p>note 3 : <a>hello <i>three</i></a></p>
<note id="test4">hello <i>four</i></note>
</section>
XSLT Code:
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
exclude-result-prefixes="#all"
version="3.0">
<xsl:output method="xml" />
<xsl:template match="#*|node()">
<xsl:copy>
<xsl:apply-templates select="#*|node()"/>
</xsl:copy>
</xsl:template>
<xsl:template match="a">
<a>
<xsl:variable name="href" select="#href" />
<xsl:choose>
<xsl:when test="$href = //note/#id">
<xsl:copy-of select="//note[#id=$href]/node()" />
</xsl:when>
</xsl:choose>
</a>
</xsl:template>
<xsl:template match="note">
<xsl:choose>
<xsl:when test="#id = //a/#href">
<xsl:apply-templates select="node" />
</xsl:when>
<xsl:otherwise>
<xsl:copy>
<xsl:apply-templates select="#*|node()"/>
</xsl:copy>
</xsl:otherwise>
</xsl:choose>
</xsl:template>
</xsl:stylesheet>

Answer 1

Whether it's efficient or not depends on how smart the optimizer in your XSLT processor is. Saxon-EE will do a pretty good job on this, Saxon-HE less so.
If you want to make it efficient on all processors, use keys. Replace an expression like //note[#id=$href] with a call on the key() function. Declare the key as
<xsl:key name="k" match="note" use="id"/>
and then you can get the matching nodes using key('k', $href).
The xsl:when test="$href = //note/#id" is redundant, as xsl:copy-of will do nothing if nothing is selected.
In the note template, I'm not sure what
<xsl:when test="#id = //a/#href">
<xsl:apply-templates select="node" />
</xsl:when>
is trying to achieve, because you don't have any elements named "node". If the aim is to avoid processing a note element at this stage if it was already processed from an a element, then you could build another index with
<xsl:key name="a" match="a" use="1"/>
and replace test="#id = //a/#href" with test="key('a', #href)"