help:enum syntax
When searching by enums, the following variation in search parameters may be used. For all of the following, substitute NAME for the name of the enum attribute.
NAME
Searches for enum values by name instead of by integer. Multiple enum values can be passed separated by spaces.
NAME_not
Excludes enum values by name instead of by integer. Multiple enum values can be excluded separated by spaces.
NAME_id
All variations of this parameter are handled the same as numeric attributes (Help:Number syntax).