code: function (id, addOn, dependencies) {
          this.items.push(addOn);
          this.lookup[id] = { instance: addOn, dependencies: dependencies };
  
          return addOn;
        }
docs: Adds a instance of the add-on by it's short name.
  
  @method add
  @param {String} id Short name/id for the add-on.
  @param {tinymce.Theme/tinymce.Plugin} addOn Theme or plugin to add.
  @return {tinymce.Theme/tinymce.Plugin} The same theme or plugin instance that got passed in.
  @example
  // Create a simple plugin
  tinymce.create('tinymce.plugins.TestPlugin', {
  TestPlugin: function(ed, url) {
  ed.on('click', function(e) {
  ed.windowManager.alert('Hello World!');
  });
  }
  });
  
  // Register plugin using the add method
  tinymce.PluginManager.add('test', tinymce.plugins.TestPlugin);
  
  // Initialize TinyMCE
  tinymce.init({
  ...
  plugins: '-test' // Init the plugin but don't try to load it
  });