code: def add_alias(self, alias, source, clean=True):
          
          if clean:
              alias = self.catalog.clean_entry_name(alias)
          self.add_quantity(self._KEYS.ALIAS, alias, source)
          return alias
docs: Add an alias, optionally 'cleaning' the alias string.
  
          Calls the parent `catalog` method `clean_entry_name` - to apply the
          same name-cleaning as is applied to entry names themselves.
  
          Returns
          -------
          alias : str
              The stored version of the alias (cleaned or not).