First of all, thanks for the XML module.  It is pretty close to being able to 
replace my copy of XML Spy.  However, the one major feature that is missing is 
the ability to do XSL transformations from within the editor.  I would image 
that this functionality would be invoked by a right-click on the XML document 
that said Transform (and an additional menu item that said Transform 
Using...  At that point the code would transform the XML document with the 
XSL document referenced by the XML document and display it in a new XML 
window. If the XML document didn't reference a XSL document, then it would 
prompt the user to assign an XSL document to the active XML document (in 
memory, meaning it wouldn't actually put the XSL ref in to the XML document).  
I would imagine that the addition of this functionality would be accompanied 
by upgrades in the text editor to include code completion for the xsl 
namespace tags.