add (OpenID::NamespaceMap)

    # File lib/openid/message.rb, line 510
        def add(namespace_uri)
          # see if this namepace is already mapped to an alias
          _alias = @namespace_to_alias[namespace_uri]
          return _alias if _alias

          # Fall back to generating a numberical alias
          i = 0
          while true
            _alias = 'ext' + i.to_s
            begin
              add_alias(namespace_uri, _alias)
            rescue IndexError
              i += 1
            else
              return _alias
            end
          end

          raise StandardError, 'Unreachable'
        end