Better support for editing XML and XSL

[Friedrich W. H. Kossebau]

Hi KDevelopers,

congrats to (and thank you for) the latest release, and hope you in Vienna 
have a nice and productive time! I wished I could be with you over there, as I 
have some more needs within KDevelop these days:

I now and then do stuff with XML and XSL, of course as much as possible in 
KDevelop :) And thus I would like to have some more support, wrt code 
completion, schema compliance, infos in tooltips on elements and attributes, 
etc.

For XSL I could additionally think of a tool to test what rules would be 
matched for a given element, that would be quite handy.

So, is there anything I can start from, that $search_engine missed?
If not, what plugin templates would I start from for the XML syntax support, 
and which tutorial is the best for me?
Is there any existing plugin which would serve as good code to copy from?

Cheers
Friedrich