Action-expression: action to be performed, e.g., operation calls
that increment attribute values. Events may take arguments
(entry
, exit
, do
take no arguments).
Triggerless transitions have no event between two states in the state
diagram; state change occurring when the internal actions in a state
is completed. When all the actions in a state are performed a
transition without an external event will automatically be
triggered. Action-expressions follow the ``/'' in state diagrams.