code: def check_siblings(graph, outputs):
      
      siblings = set()
      for node in outputs:
          siblings |= graph.siblings(node)
  
      siblings = {node.path for node in siblings}
      missing = siblings - {node.path for node in outputs}
  
      if missing:
          msg = (
              'Include the files above in the command '
              'or use the --with-siblings option.'
          )
          raise click.ClickException(
              'There are missing output siblings:\n\n'
              '\t{0}\n\n{1}'.format(
                  '\n\t'.join(click.style(path, fg='red') for path in missing),
                  msg,
              ),
          )
      return outputs
docs: Check that all outputs have their siblings listed.