# File lib/openid/message.rb, line 424
    def get_aliased_arg(aliased_key, default=nil)
      if aliased_key == 'ns'
        return get_openid_namespace()
      end

      ns_alias, key = aliased_key.split('.', 2)
      if ns_alias == 'ns'
        uri = @namespaces.get_namespace_uri(key)
        if uri.nil? and default == NO_DEFAULT
          raise KeyNotFound, "Namespace #{key} not defined when looking "\
                             "for #{aliased_key}"
        else
          return (uri.nil? ? default : uri)
        end
      end

      if key.nil?
        key = aliased_key
        ns = nil
      else
        ns = @namespaces.get_namespace_uri(ns_alias)
      end

      if ns.nil?
        key = aliased_key
        ns = get_openid_namespace
      end

      return get_arg(ns, key, default)
    end