Should processors work with references? I would think that they should, 
but the following fails. (My backmatter page numbers need to be marked 
to distinguish them from bodymatter pages. I can automate applying a 
processor based on the location for index register entries, but not for 
references.)

    \defineprocessor[xx][style=slanted,after=n]
    \starttext
    \section[xxx]{Processor testing}
    Why cannot a processor be applied to a reference? \at[xx->xxx]
    \stoptext

-- 
Rik