XSL Extension

I'm documenting the new XSL extension and needed a little clarification on the two XSL functions in the PHP namespace [function() and functionString()]. In what case would either of these XSL functions be called? As I understand it php:function() only allows string parameters to the handling PHP function whereas php:functionString() allows passing element values to the function. Examples: <xsl:value-of select="php:function('date', 'r')"/> Outputs the RFC formatted date (current date/time) <xsl:value-of select="php:functionString('date', 'r', date)"/> Outputs the RFC formatted date of the <date> element as the unix timestamp I just wanted to be sure of what I've gathered from testing and the source that the usage of both functions is correct. Any other information would be appreciated. Thanks, Kenneth