- clarify Enum validation rules, fixes #3904
- clarify Enum validation rules, fixes #3904

Change-Id: I221f161ae77ee1b9487329330bc520ab65e97611

wujuguang/sqlalchemy,j5int/sqlalchemy,monetate/sqlalchemy,j5int/sqlalchemy,graingert/sqlalchemy,zzzeek/sqlalchemy,wujuguang/sqlalchemy,sqlalchemy/sqlalchemy,graingert/sqlalchemy,monetate/sqlalchemy