Add `ProgramStateManager` documentation for when to raise an error.
@@ -59,6 +59,8 @@ class ProgramStateManager(metaclass=abc.ABCMeta):
Raises:
ProgramStateManagerStateNotFoundError: If there is no program state for
the given `version`.
+ ProgramStateManagerStructureError: If `structure` does not match the value
+ loaded for the given `version`.
"""
raise NotImplementedError
