code: function create(opt_options) {
    function runInclude(file, encoding, callback) {
      if (file.isNull()) {
        return callback(null, file);
      }
      if (file.isStream()) {
        this.emit('error', new PluginError(PLUGIN_NAME,
            'Streams not supported!'));
      }
      if (file.isBuffer()) {
        addIncludesToFile(file, opt_options).then((file) => {
          return callback(null, file);   
        })
        .catch(() => {
          return callback(null, file); 
        });
      }
    }
    var rv = function() {
      return through.obj(runInclude);
    };
    return rv; 
  }
docs: Imports the required AMP custom-element script tags into an AMP document.
  
  @param {Object} opt_options Configurations options, currently:
  placeholder: Overrides the default placeholder.
  mode: Overrides the default mode (MODES.PLACEHOLDER);
  @return {!Transform} The created stream.Transform object.