docs: def _draw_messages(self, painter):
          """
          Draw messages from all subclass of CheckerMode currently
          installed on the editor.
  
          :type painter: QtGui.QPainter
          """
          checker_modes = []
          for m in self.editor.modes:
              if isinstance(m, modes.CheckerMode):
                  checker_modes.append(m)
          for checker_mode in checker_modes:
              for msg in checker_mode.messages:
                  block = msg.block
                  color = QtGui.QColor(msg.color)
                  brush = QtGui.QBrush(color)
                  rect = QtCore.QRect()
                  rect.setX(self.sizeHint().width() / 4)
                  rect.setY(block.blockNumber() * self.get_marker_height())
                  rect.setSize(self.get_marker_size())
                  painter.fillRect(rect, brush)