[LC] 8.3.2 The mediatype Element

http://www.w3.org/TR/xforms11/#ui-commonelems-mediatype

We now have

   <output ref="piccy" mediatype="image/png">

and

   <output ref="piccy"><mediatype ref="../type"/></output>

It would be better if it used @value instead of @ref, since then you
could write:

   <output ref="data"><mediatype value="concat('image/', type)"/></output>

Even better, since the attribute is completely new, is to do away with
the mediatype element altogether:

   <output ref="data" mediatype="../type"/>

(which would require
   <output ref="data" mediatype="'image/png'">
for the literal case.)

The way that mediatype@ref has two different purposes depending on its
parent element is nasty.