'Should return the set of matches for :param:\'location` and :param:`query`.
The search must be performed over all entries if :param:`candidates` is
None otherwise only over the items in candidates.
:param:`location` is one of the items in :member:`SearchQueryParser.DEFAULT_LOCATIONS`.
:param:`query` is a string literal.
:return: None or a subset of the set returned by :meth:`universal_set`.'

def get_matches(self, location, query, candidates=None):

    return set([])
