UML14 — Protocol state diagrams issue

Summary: UML still does not develop the meaning and the semantics of protocol state diagrams. Protocol state diagrams are close to be supported by the UML metamodel, which still requires some smooth evolutions.
In a protocol state diagram, a transition related to an operation expresses that the operation can be invoked under the origin state and the "guard" condition, and that under these preliminary context, the operation invocation will lead to the destination state, under a certain post-condition.
A protocol state diagram can be entirely transformed into pre and post conditions for the involved methods.
There is a need to add post-condition to transitions for protocol state diagram.
Suggestion : add a new aggregation from transition to "Guard", called post.

Considered and declined.