docs: def add_marker(self, marker):
          """
          Adds the marker to the panel.
  
          :param marker: Marker to add
          :type marker: pyqode.core.modes.Marker
          """
          self._markers.append(marker)
          doc = self.editor.document()
          assert isinstance(doc, QtGui.QTextDocument)
          block = doc.findBlockByLineNumber(marker._position)
          marker.block = block
          d = TextDecoration(block)
          d.set_full_width()
          if self._background:
              d.set_background(QtGui.QBrush(self._background))
              marker.decoration = d
          self.editor.decorations.append(d)
          self.repaint()