You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: dtd.rb
    path of file: ./repos/truffleruby/lib/gems/gems/rexml-3.2.5/lib/rexml/dtd
    
    the code of the file until where you have to start completion: # frozen_string_literal: false
require_relative "elementdecl"
require_r
    
      def Parser.parse( input )
        case input
        when String
          parse_helper input
        when File
          parse_helper input.read
        end