OPC 10000-5 B.4.5 states that (my emphasis):
Each Transition shall have a BrowseName which is unique within the StateMachine and may have a TransitionNumber which shall also be unique across all Transitions defined in the StateMachine.
I am implementing a companion specification which leaves TransitionNumber undefined - which seems OK given the "may" clause above. But since TransitionNumber has a Mandatory modelling rule, I still need to implement this property. Am I correct that I should then return a bad status code when the value of this property is read? What is the correct status code to return?
This needs a mantis issue. The current model makes TransitionNumber Node mandatory and that single sentence looks like an error. If the TransitionNumber is optional the the spec needs to define the correct error code to return if it is not supported but for now you should assume it is Mandatory.
If the PackML specification missing the TransitionNumbers then it needs an update to add them.