# File lib/openid/message.rb, line 78
    def Message.register_namespace_alias(namespace_uri, alias_)
      if @@registered_aliases[alias_] == namespace_uri
          return
      end

      if @@registered_aliases.values.include?(namespace_uri)
        raise NamespaceAliasRegistrationError,
          'Namespace uri #{namespace_uri} already registered'
      end

      if @@registered_aliases.member?(alias_)
        raise NamespaceAliasRegistrationError,
          'Alias #{alias_} already registered'
      end

      @@registered_aliases[alias_] = namespace_uri
    end