BPMN2 — Grouping message flow in Collaboration

Message flow can be grouped in Choreography and Conversation, and should
be in Collaboration also. For example, a collaboration participant
might have a process with a call activity that send/receives many
messages. The modeler should be able to show these as a single line
between the activity and the other participant, as in a conversation.
otherwise, the modeler can only show the most detailed view of the
interaction, with every lowest level message flow in the diagram.

The resolution of issue 14564 will resolve this issue
Disposition: Duplicate