Requests a hint about the valid range of values for the state of action.
If NULL is returned it either means that the action is not stateful or that there is no hint about the valid range of values for the state of the action.
If a glib.Variant array is returned then each item in the array is a possible value for the state. If a glib.Variant pair (ie: two-tuple) is returned then the tuple specifies the inclusive lower and upper bound of valid values for the state.
In any case, the information is merely a hint. It may be possible to have a state value outside of the hinted range and setting a value within the range may fail.
The return value (if non-NULL) should be freed with Variant.unref when it is no longer required.