The type of shape, fixing the type of state
The identifier state states, or undefined where shape declares no id member or state states none
TraceError Where state doesn't conform to shape, where a deferred
definition reaches itself with no link to break the cycle, or where it states a target that doesn't narrow the
one the link it is reached through overrides, as a re-pointed target must extend the one it replaces
Retrieves the identifier of a state.