code: function (fileContents, onConfig) {
              var details = parse.findConfig(fileContents),
                  config = details.config;
  
              if (config) {
                  config = onConfig(config);
                  if (config) {
                      return transform.serializeConfig(config,
                                                fileContents,
                                                details.range[0],
                                                details.range[1],
                                                {
                                                  quote: details.quote
                                                });
                  }
              }
  
              return fileContents;
          }
docs: Modify the contents of a require.config/requirejs.config call. This
  call will LOSE any existing comments that are in the config string.
  
  @param  {String} fileContents String that may contain a config call
  @param  {Function} onConfig Function called when the first config
  call is found. It will be passed an Object which is the current
  config, and the onConfig function should return an Object to use
  as the config.
  @return {String} the fileContents with the config changes applied.