code: def add_channels_to_list(self, l, add_ref=False):
          
          l.clear()
  
          l.setSelectionMode(QAbstractItemView.ExtendedSelection)
          for chan in self.chan_name:
              item = QListWidgetItem(chan)
              l.addItem(item)
              
          if add_ref:
              item = QListWidgetItem('_REF')
              l.addItem(item)
docs: Create list of channels (one for those to plot, one for ref).
  
          Parameters
          ----------
          l : instance of QListWidget
              one of the two lists (chan_to_plot or ref_chan)