obsolete: a key or tag which is no longer found in the database
proposed: the key or tag has been proposed to be used (but not yet approved) and usage of this tagging is minimal (1)
undefined or (empty): unclear situation (this may be actually useful in case where data item has invalid value and it is not entirely clear which one should be used and someone is not interested in editing data items)
voting: the key or tag is currently being voted on as part of the approval process