code: function ( deltaTime ) {
  
  		deltaTime *= this.timeScale;
  
  		var actions = this._actions,
  			nActions = this._nActiveActions,
  
  			time = this.time += deltaTime,
  			timeDirection = Math.sign( deltaTime ),
  
  			accuIndex = this._accuIndex ^= 1;
  
  		// run active actions
  
  		for ( var i = 0; i !== nActions; ++ i ) {
  
  			var action = actions[ i ];
  
  			action._update( time, deltaTime, timeDirection, accuIndex );
  
  		}
  
  		// update scene graph
  
  		var bindings = this._bindings,
  			nBindings = this._nActiveBindings;
  
  		for ( var i = 0; i !== nBindings; ++ i ) {
  
  			bindings[ i ].apply( accuIndex );
  
  		}
  
  		return this;
  
  	}
docs: advance the time and update apply the animation