code: function () {
  		this._super.onenter ();
  		if ( this.box.pageY < window.innerHeight ) {
  			this._hilite ();
  		} else {
  			this.tick.time ( function () {
  				this._hilite ();
  			}, 200 );
  		}
  	}
docs: Visible code get's highlighted now while unseen code runs on a timeout.
  The internal async thing in Prism doesn't seem to work as advertised...