The number.append Activity as entry Behavior for the PartialDial State

If you've been following this tutorial you'll already know the sequence of InitialNode, ReadSelfAction, and ReadStructuralFeatureAction to get at number:Number - noting that the context class here is Dialer. Then a CallOperationAction is used to execute the operation append(n:int).

But where does the value for the input Parameter corresponding to that ActivityParameterNode n:int come from? It is "magically" matched against the Parameter of the Operation digit(n:int) from Dialer of the CallEvent trigger that was used on the Transitions that enter the Dialing State!

Now let's see how append(n:int) works