[Zope-CMF] add Metadata element to existing types

[Siegfried Stepke]

Hello,

although I found lots of information regarding adding new CMF-Types with 
their own properties I didn't find anything about adding a totally new 
element in the metadata to show up in the full_metadata_edit_form ...

I succeeded in creating a new element in the portal_metadata tool; it 
shows up there and I can set its default or content-type-specific 
settings. But I don't know what to do to let it show up in the documents 
meta-data edit forms...

Is this possible? (or are only the standard metadata elements supported?)
Is this possible for the default portal-types?
Do I have to create a new "custom/full_metadata_edit_form"?
  Which code would have to be integrated there for a subject-like element?

The goal is to integrate more metadata fields like target_audience_level, 
client_category, etc. to be able to create nice topics specific to that 
data and even more...

I really searched a lot in the docs and archives and found a lot similar 
questions but all answers just pointed to new types with properties - not 
metadata.

thanks for any help!

regards,
siegfried