When several transitions can be chosen in the GUI with a 'select', the user cannot see which values are until the transitions are taken. The labels in the GUI should tell which values are taken. This is particularly relevant for synchonizations on channels in arrays, eg, c[i]! where 'i' is (or is not) taken from select. The MSC should also reflect this.
I think Alexandre is refering to the list of enabled transition in the simulator.