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<h1>saxon:explain</h1>
<p>This attribute may be set on any instruction in the stylesheet, including a literal
result element, though the recommended use is to set it on an <code>xsl:template</code> or <code>xsl:function</code>
declaration. The permitted values
are "yes" and "no". If the value is "yes", then at compile time Saxon outputs (to the standard error
output) a representation of the optimized expression tree for the template or function containing that instruction. The tree is
represented by indentation. For example, consider this source code:</p>
<div class="codeblock"
style="border: solid thin; background-color: #B1CCC7; padding: 2px">
<pre>
<code>
<xsl:variable name="p" select="0"/>
<xsl:template match="/" saxon:explain="yes" xmlns:saxon="http://saxon.sf.net/" exclude-result-prefixes="saxon">
<a>
<xsl:choose>
<xsl:when test="$p != 0"><xsl:value-of select="1 div $p"/></xsl:when>
<xsl:otherwise>12</xsl:otherwise>
</xsl:choose>
</a>
</xsl:template></code>
</pre>
</div>
<p>This produces the output:</p>
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style="border: solid thin; background-color: #B1CCC7; padding: 2px">
<pre>
<code>Optimized expression tree for template at line 8 in file:/e:/temp/test.xsl:
<directElement name="a" validation="skip">
<valueOf>
<literal value="12" type="xs:string"/>
</valueOf>
</directElement></code>
</pre>
</div>
<p>This indicates that the template has been reduced to an instruction to create an element with name <code>a</code>,
whose content is a single text node holding the string "12". This is because Saxon has established at
compile time that it will always take the "otherwise" branch of the <code>xsl:choose</code>
instruction. There is no <code>xsl:value-of</code> instruction in the source code, but the literal
text node "12" is compiled to the same code as if the user had written
<code><xsl:value-of select="'12'"/></code></p>
<p>To get this output for all templates and functions in the stylesheet, you can use the <code>-explain</code>
option on the command line.</p>
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