code: function () {
      var el;
      el = document.createElement('a-entity');
      el.play = this.wrapPlay(el.play);
      el.setAttribute('mixin', this.data.mixin);
      el.object3D.visible = false;
      el.pause();
      this.container.appendChild(el);
      this.availableEls.push(el);
    }
docs: Add a new entity to the list of available entities.