docs: def add_line(self, p1, p2, char_length):
          """
          Add a line to the list. Check if the nodes already exist, and add them
          if not.
  
          Return the line index (1-indixed, starting with 1)
          """
          p1_id = self.get_point_id(p1, char_length)
          p2_id = self.get_point_id(p2, char_length)
          self.Lines.append((p1_id, p2_id))
          return len(self.Lines)