code: def add_boundary(self, p1, p2, btype):
          
          index = self.add_line(p1, p2, self.char_lengths['boundary'])
          # self.Boundaries.append((p1_id,p2_id,btype))
          self.BoundaryIndices.append(index)
          self.Boundaries.append((p1, p2, btype))
docs: Add a boundary line