code: def in_labelset(xmrs, nodeids, label=None):
      
      nodeids = set(nodeids)
      if label is None:
          label = xmrs.ep(next(iter(nodeids))).label
      return nodeids.issubset(xmrs._vars[label]['refs']['LBL'])
docs: Test if all nodeids share a label.
  
      Args:
          nodeids: iterable of nodeids
          label (str, optional): the label that all nodeids must share
      Returns:
          bool: `True` if all nodeids share a label, otherwise `False`