> In what way did you use (do you use?) the domain fields of PKT type 2.2?

Wherever domains were specified, they got plugged in.  When multiple
messages with different domains go to the same packet, one PKT is created
for each domain.
 
> As far as I can see, they are of limited value since they relate to the 
> whole PKT file rather than to individual messages.

True: then again, the whole address in a .PKT is just as useful, since for
the most part, .PKTs are properly created with each message being at least
3D and usually 4D (with .0 being implied).

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