An XSL processors parses an XML source and tries to find a matching template rule.
If it does, instructions inside matching template are evaluated.
File: Data.xml
<data>
<bold>Hello, world.</bold>
<red>I am </red>
<italic>fine.</italic>
</data>
File: Transform.xslt
<?xml version="1.0"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match="bold">
<paragraph>
<b>
<xsl:value-of select="."/>
</b>
</paragraph>
</xsl:template>
<xsl:template match="red">
<paragraph style="color:red">
<xsl:value-of select="."/>
</paragraph>
</xsl:template>
<xsl:template match="italic">
<paragraph>
<i>
<xsl:value-of select="."/>
</i>
</paragraph>
</xsl:template>
</xsl:stylesheet>
Output:
<?xml version="1.0" encoding="UTF-8"?>
<paragraph><b>Hello, world.</b></paragraph>
<paragraph style="color:red">I am </paragraph>
<paragraph><i>fine.</i></paragraph>