code: def add(self, start, end):
          
          assert start <= end
          self._intervals.append((start, end))
docs: Add the start and end offsets of a matching read.
  
          @param start: The C{int} start offset of the read match in the subject.
          @param end: The C{int} end offset of the read match in the subject.
              This is Python-style: the end offset is not included in the match.