def existing_terms(self, ixreader, termset=None, reverse=False, phrases=True):
        
        if termset is None:
            termset = set()
        self._existing_terms(ixreader, termset, reverse=reverse, phrases=phrases)
        return termset
Returns a set of all terms in this query tree that exist in the index
dataset/ETHPy150Open dokipen/whoosh/src/whoosh/query.py/Query.existing_terms