Feature request already discussed with Ralf:

Example call:
rest/data/user?ad_domain=example.com&@fields=pictures.type

The pictures attribute per user item is an array.
Because of this we currently cannot include a picture attribute directly 
in the response (pictures.type) but we would like to do so.

Please include this feature during the next good occasion.

Ralf,

I don't quite understand this.
I assume you have a patch for it. Assigning to you.

Currently in the REST-API you can request transitive properties, e.g. when querying issue you could use @fields=priority.order (given that the priority table has an 'order' property). This currently only works for Link properties not for Multilink properties.
In our schema there is field 'pictures' in the user class linking to files with pictures of the user. You cannot currently request properties of pictures using @fields.

And, no, I don't have a patch yet :-)

Thanks for assigning to me!