Hi Martin,

I would also like to point you to an article written by Aaron Skonnard for 
MSDN magazine in March 2002. 

See: http://msdn.microsoft.com/msdnmag/issues/02/03/xml/

"The XSLT 1.0 specification defines two types of extensions: extension 
elements and extension functions. Both types of extensions provide additional 
functionality to the standard language and can be used like any other XSLT 
1.0 element (these include xsl:transform, xsl:template, xsl:value-of, and so 
on) or XPath 1.0/XSLT 1.0 function (such as string, substring-before, sum, 
document, and so forth)."

Aaron continues to describe how extension elements work, but provides no 
real implementation details. Curiously he also describes a mechanism for 
getting and setting properties.

"Properties are accessed in XSLT by prefixing the property name with either 
get- or put- followed by parentheses. eg. get-age(), put-age(33)"

I got the property get- working fine, but I have not been able to get the 
property put- funtion right. At least one other article talks of set- rather 
than put- and Microsoft documentation only ever mentions the get- method.