MachineActionInput
One action of a statechart, run on a transition or when a state is entered or left: set_slot writes a value into a slot, clear_slot resets it to its default, pop_slot removes the first item of a list slot, inject_context writes a keyed context entry, say speaks a template through before_speak, emit_event sends an event to a Process (not available yet), and tag adds labels to the Call.
A union of 7 variants.