code: func (q *MultiMatchQuery) CutoffFrequency(cutoff float64) *MultiMatchQuery {
  	q.cutoffFrequency = &cutoff
  	return q
  }
docs: // CutoffFrequency sets a cutoff value in [0..1] (or absolute number >=1)
  // representing the maximum threshold of a terms document frequency to be
  // considered a low frequency term.