Check attribute existance : attribute « XPath « XML Tutorial

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2. XPath
3. attribute

File: Data.xml

<?xml version="1.0" standalone="yes"?>
<poem author="jm" year="1667">
  <verse>line 1</verse>
  <verse>line 2</verse>
  <verse>line 3</verse>
  <verse>line 4</verse>
</poem>

File: Transform.xslt

<?xml version="1.0" standalone="yes"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  version="1.0">
  <xsl:output method="text" />
  <xsl:template match="poem">
    <xsl:if test="@author='jm'">1. The poem's author is jm.</xsl:if>
  </xsl:template>
</xsl:stylesheet>

Output:

1. The poem's author is jm.