docs: def import_command(dest, src, name, api=None, filter_symbol=None):
      """Import Command `name` and its dependencies from Registry `src`
      to Registry `dest`
  
      :param Registry dest: Destination Registry
      :param Registry src: Source Registry
      :param str name: Name of Command to import
      :param str api: Prefer to import Types with api name `api`, or None to
                      import Types with no api name
      :param filter_symbol: Optional filter callable
      :type filter_symbol: Callable with signature
                           ``(symbol_type:str, symbol_name:str) -> bool``
      """
      if not filter_symbol:
          filter_symbol = _default_filter_symbol
      cmd = src.commands[name]
      for x in cmd.required_types:
          if not filter_symbol('type', x):
              continue
          import_type(dest, src, x, api, filter_symbol)
      dest.commands[name] = cmd