<?xml version="1.0" ?>
<description>description
    <para>Paragraph number 1</para>
    <para>Paragraph number 2</para>
    <para>Paragraph number 3</para>
</description>

<?xml version="1.0" encoding="UTF-8" ?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="2.0">
<xsl:template match="/description/para[3]">
&lt;para>Modify paragraph #3&lt;/para>
</xsl:template>
<xsl:template match="/">
    <xsl:apply-templates />
</xsl:template>
</xsl:stylesheet>

xmlpatterns test.xsl test.xml

--> 

description
    Paragraph number 1
    Paragraph number 2
    Paragraph number 3

xalan -xsl test.xsl  -in test.xml

-->

<?xml version="1.0" encoding="UTF-8"?>description
    Paragraph number 1
    Paragraph number 2    
&lt;para&gt;Modify paragraph #3&lt;/para&gt;

description/para[3]

 xmlpatterns test.xq test.xml 
-->
<para>Paragraph number 3</para>