docs: def mousePressEvent(self, e):
          """
          Starts selecting
          """
          self._selecting = True
          self._sel_start = e.pos().y()
          start = end = TextHelper(self.editor).line_nbr_from_position(
              self._sel_start)
          self._start_line = start
          TextHelper(self.editor).select_lines(start, end)