docs: def identifier(self):
          """Set the identifier of the current MOC.
  
          The new identifier should be given after this option.
  
          ::
  
              pymoctool ... --id 'New MOC identifier' --output new_moc.fits
          """
  
          if self.moc is None:
              self.moc = MOC()
  
          self.moc.id = self.params.pop()