docs: def insert(self, seq):
          """
          Populates the DB from a sequence of strings, ERASING PREVIOUS STATE.
  
          :param seq: an iterable
  
          """
          # erase previous elements and make defaultdict for easier insertion.
          self._els_idxed = defaultdict(lambda: defaultdict(set))
          if type(seq) is str:
              raise ValueError('Provided argument should be a sequence of strings'
                               ', but not a string itself.')
          for el in seq:
              if type(el) is not str:
                  raise ValueError('Element %s is not a string' % (el,))
              for gram in make_unique_ngrams(el, self.idx_size):
                  self._els_idxed[gram][len(el)].add(el)
  
          # convert defaultdict to dict so as to not increase size when checking
          # for presence of an element
          self._finalize_db()