# File htree/elem.rb, line 87
    def get_subnode(index)
      case index
      when String
        name = Name.parse_attribute_name(index, DefaultContext)
        @stag.get_attribute(name.universal_name)
      when Name
        @stag.get_attribute(index.universal_name)
      when Integer
        @children[index]
      else
        raise TypeError, "invalid index: #{index.inspect}"
      end
    end