Function: Registers a meta key for terms.

Function: Unregisters a meta key for terms.

Function: Determines whether a taxonomy term exists.

Function: Checks if a term is an ancestor of another term.

Function: Sanitizes all term fields.

Function: Removes an already registered taxonomy from an object type.

Function: Retrieves object IDs of valid taxonomy and term.

Function: Given a taxonomy query, generates SQL to be appended to a main query.