Calling PHP Functions from XSLT Stylesheets

$xslt = new XSLTProcessor();
$xslt->registerPHPFunctions();

<?xml version="1.0" ?>
<xsl:stylesheet version="1.0"
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:php="http://php.net/xsl"
    xsl:extension-element-prefixes="php">
 
<xsl:template match="/">
    <xsl:value-of select="php:function('strftime', '%c')" />
</xsl:template>
 
</xsl:stylesheet>