The usage state for this entity. This object refers to an entity's ability to service more physical entities in a containment hierarchy. A value of 'idle' means this entity is able to contain other entities but that no other entity is currently contained within this entity. A value of 'active' means that at least one entity is contained within this entity, but that it could handle more. A value of 'busy' means that the entity is unable to handle any additional entities being contained in it. Some entities will exhibit only a subset of the usage state values. Entities that are unable to ever service any entities within a containment hierarchy will always have a usage state of 'busy'. Some entities will only ever be able to support one entity within its containment hierarchy and will therefore only exhibit values of 'idle' and 'busy'.