%service% Incoming/Outgoing only? (req:Possible for Header?)

[Perez]

Is something like %service% available for Header.html, for message styles? I was looking at the docs, and %service% is listed as only available for incoming/outgoing messages; would it be possible to make a similar keyword available for Header.html (that either defaults to in or out, or is two keywords, %incomingservice% and %outgoingservice%) ?