How to force prefixes instead of expanded qnames?

Hi there!

I guess this must have come up before, but I can't find it.

I get this kind of a result which works fine, but is a bit more
difficult to read than necessary:

<Repository xmlns:oai="http://www.openarchives.org/OAI/2.0/"
            xmlns="http://www.openarchives.org/OAI/2.0/static-repository"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xmlns:mpx="http://www.mpx.org/mpx"
            xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/static-re
pository
   http://www.openarchives.org/OAI/2.0/static-repository.xsd">
...
B B  B  B  B  <oai:metadata>
B B  B  B  B  B  B <mpx:multimediaobjekt
xsi:schemaLocation="http://www.mpx.org/mpx
file:/c:/cygwin/home/Mengel/usr/levelup/lib/mpx-lvl2.v2.xsd"
B B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B 
B exportdatum="2010-04-19T16:39:14"
B B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B mulId="7216">
B B  B  B  B  B  B  B  <bearbDatum xmlns="http://www.mpx.org/mpx">12.12.2005
14:32:13</bearbDatum>
B B  B  B  B  B  B  B  <multimediaFarbe
xmlns="http://www.mpx.org/mpx">farbig</multimediaFarbe>
B B  B  B  B  B  B  B  <multimediaFormat xmlns="http://www.mpx.org/mpx">RF
(6x6 cm)</multimediaFormat>
...

I would prefer having the namespace written as a prefix like in
<mpx:multimediaobjekt>.

This is an xslt 2 transformation and I am using copy-of to create
those elements where I don't like the output.

Thanks!
Maurice