How to return Item's XML properly in an xsl extension function? How to return node sets in C# in order to use it in XSLT?
You should use property-like methods with get_ or set_ prefixs to return Item's XML, for example if the property is named ItemID you should use the following statements
get_ItemID()
and
set_ItemID()
This is the way .Net Framework converts properties to methods.
If you wish to return an Item set that will be possible to loop through, you need to return XpathNodeIterator: