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			}
			items[ item ] = interval; // Tether item to original pulseint. Used in removeItem & setPaused(false).
			if (!timers[ interval ]) {
				addPulse( interval );
				itemCounts[ interval ] = 1;
			}
			else {
				itemCounts[ interval ] ++;
			}
			// Report IManageable instances to registered managers
			if (item is IManageable) {
				for each (var manager:IManager in managers)
					manager.reserve( item as IManageable );
			}
			return true;
		}
		
		/**
		 * Removes an item from the queue and removes its pulse timer if
		 * the queue is depleted.
		 * 
		 * @param item		Any IUpdatable previously added that wishes 
		 * 					to stop receiving update calls.
		 * 					
		 * @return			Returns false if the item was not in the engine.
		 * 
		 * @see #addItem()
		 */
		public static function removeItem( item:IUpdatable ):Boolean
		{
			if (items[ item ]==null)
				return false;
			var interval: int = items[ item ];
			if ( -- itemCounts[ interval ] == 0 ) {
				removePulse( interval );
				delete itemCounts[ interval ];
			}
			delete items[ item ];
			delete addQueue[ item ]; // * see note following update
			// Report IManageable item removal to registered managers.
			if (item is IManageable) {
				for each (var manager:IManager in managers) 
					manager.release( item as IManageable );
			}
			return true;
		}
		
		/**
		 * Removes all items and resets the engine, 
		 * or removes just items running on a specific pulse.
		 * 
		 * @param pulseInterval		Optionally filter by a specific pulse 
		 * 							such as ENTER_FRAME or a number of milliseconds.
		 * @return					The number of items successfully removed.
		 * @see #removeItem()
		 */
		public static function clear(pulseInterval:Number = NaN) : uint
		{
			var all:Boolean = (isNaN(pulseInterval));
			var n:Number = 0;
			for (var item:Object in items) {
				if (all || items[ item ]==pulseInterval)
					if (removeItem(item as IUpdatable)==true)
						n++;
			}
			return n;
		}
		
		/**
		 * Retrieves number of active items in the engine 
		 * or active items running on a specific pulse.
		 * 
		 * @param pulseInterval		Optionally filter by a specific pulseInterval
		 *							such as ENTER_FRAME or a number of milliseconds.
		 * 
		 * @return					Number of active items in the Engine.
		 */
		public static function getCount(pulseInterval:Number = NaN) : uint
		{
			if (!isNaN(pulseInterval))
				return (itemCounts[pulseInterval]);
			var n:Number = 0;
			for each (var count: int in itemCounts)
				n += count;
			return n;
		}
		
		/**
		 * @return			The paused state of engine.
		 * @see #setPaused()
		 */
		public static function getPaused() : Boolean {
			return paused;
		}
		
		/**
		 * Pauses or resumes all animation globally by suspending processing,
		 * and calls pause() or resume() on each item with those methods. 
		 * 
		 * <p>The return value only reflects how many items had pause() or resume()
		 * called on them, but the GoEngine.getPaused() state will change if any 
		 * pulses are suspended or resumed.</p>
		 * 
		 * @param pause				Pass false to resume if currently paused.
		 * @param pulseInterval		Optionally filter by a specific pulse 
		 * 							such as ENTER_FRAME or a number of milliseconds.
		 * @return					The number of items on which a pause() or resume()
		 * 							method was called (0 doesn't necessarily reflect
		 * 							whether the GoEngine.getPaused() state changed, it
		 * 							may simply indicate that no items had that method).
		 * @see #resume()
		 */
		public static function setPaused(pause:Boolean=true, pulseInterval:Number = NaN) : uint
		{
			if (paused==pause) return 0;
			var n:Number = 0;
			var pulseChanged:Boolean = false;
			var all:Boolean = (isNaN(pulseInterval));
			var method:String = (pause ? "pause" : "resume");
			for (var item:Object in items) {
				var pulse:int = (items[item] as int);
				if (all || pulse==pulseInterval) {
					pulseChanged = (pulseChanged || (pause ? removePulse(pulse) : addPulse(pulse)));
					// call pause or resume on the item if it has such a method.
					if (item.hasOwnProperty(method)) {
						if (item[method] is Function) {
							item[method].apply(item);
							n++;
						}
					}
				}
			}
			if (pulseChanged)
				paused = pause;
			return n;
		}
		
		// -== Private Class Methods ==-
		
		/**
		 * Executes the update queue corresponding to the dispatcher's interval.
		 * 
		 * @param event			TimerEvent or Sprite ENTER_FRAME Event
		 */
		private static function update(event:Event) : void 
		{
			var currentTime:Number = getTimer();
			var pulse:int = (event is TimerEvent ? ( event.target as Timer ).delay : ENTER_FRAME);
			lockedPulses[ pulse ] = true;
			var doLiveUpdate:Boolean = (liveManagers > 0);
			var updated:Array;
			if (doLiveUpdate) updated = []; // syncs the live manager list to items actually updated
			for (var item:* in items) {
				if (items[ item ]==pulse && !addQueue[ item ]) {
					(item as IUpdatable).update(currentTime);
					if (doLiveUpdate) updated.push(item);
				}
			}
			lockedPulses[ pulse ] = false;
			if (delayedPulses[ pulse ]) {
				for (item in addQueue) 
					delete addQueue[ item ];
				delete delayedPulses[ pulse ];
			}
// updateAfterEvent() should not be needed as long as items follow tight-syncing instructions in GoItem.update() documentation.
//			if (pulse!=ENTER_FRAME) (event as TimerEvent).updateAfterEvent();
			if (doLiveUpdate)
				for each (var manager:Object in managers)
					if (manager is ILiveManager)
						(manager as ILiveManager).onUpdate(pulse, updated, currentTime);  // * see note
		}
// * note: In one rare case that has not been reported yet but is theoretically possible, the 'updated' list 
// passed could contain already-released items. This could only happen if the item is removed & released 
// just after the main update cycle but before the the doLiveUpdate() routine runs. If you encounter this issue
// please report it to the GoASAP mailing list, it's too involved to bother with before it's a problem.

		/**
		 * Creates new timers when a previously unused interval is specified,
		 * and tracks the number of items associated with that interval.
		 * 
		 * @param pulse			The pulseInterval requested
		 * @return				Whether a pulse was added
		 */
		private static function addPulse(pulse : int) : Boolean
		{
			if (pulse==ENTER_FRAME) {
				if (!pulseSprite) {
					timers[ENTER_FRAME] = pulseSprite = new Sprite();
					pulseSprite.addEventListener(Event.ENTER_FRAME, update);
				}
				return true;
			}
			var t:Timer = timers[ pulse ] as Timer;
			if (!t) {
				t = timers[ pulse ] = new Timer(pulse);
				(timers[ pulse ] as Timer).addEventListener(TimerEvent.TIMER, update);
				t.start();
				return true;
			}
			return false;
		}
		
		/**
		 * Tracks whether a removed item was the last one using a timer 
		 * and if so, removes that timer.
		 * 
		 * @param pulse			The pulseInterval corresponding to an item being removed.
		 * @return				Whether a pulse was removed
		 */
		private static function removePulse(pulse : int) : Boolean
		{
			if (pulse==ENTER_FRAME) {
				if (pulseSprite) {
					pulseSprite.removeEventListener(Event.ENTER_FRAME, update);
					delete timers[ ENTER_FRAME ];
					pulseSprite = null;
					return true;
				}
			}
			var t:Timer = timers[ pulse ] as Timer;
			if (t) {
				t.stop();
				t.removeEventListener(TimerEvent.TIMER, update);
				delete timers[ pulse ];
				return true;
			}
			return false;
		}
	}
}