docs: def marker_for_line(self, line):
          """
          Returns the marker that is displayed at the specified line number if
          any.
  
          :param line: The marker line.
  
          :return: Marker of None
          :rtype: pyqode.core.Marker
          """
          markers = []
          for marker in self._markers:
              if line == marker.position:
                  markers.append(marker)
          return markers