@classmethod
def RegisterHelper(cls, resolver_helper):
    """Registers a path specification resolver helper.

    Args:
      resolver_helper (ResolverHelper): resolver helper.

    Raises:
      KeyError: if resolver helper object is already set for the corresponding
          type indicator.
    """
    if resolver_helper.type_indicator in cls._resolver_helpers:
        raise KeyError(
            'Resolver helper object already set for type indicator: {0!s}.'
            .format(resolver_helper.type_indicator))
    cls._resolver_helpers[resolver_helper.type_indicator] = resolver_helper
