Landing the new expando management code. Completely overhauls how data is associated with elements.

Plugins will be most interested in:
- jQuery.data(elem) -> Unique ID for the element
- jQuery.data(elem, name) -> Named data store for the element
- jQuery.data(elem, name, value) -> Saves a value to the named data store
- jQuery.removeData(elem) -> Remove the expando and the complete data store
- jQuery.removeData(elem, name) -> Removes just this one named data store

jQuery's .remove() and .empty() automatically clean up after themselves. Once an element leaves a DOM document their events are no longer intact. Thus, statements like so:
{{{
  $("#foo").remove().appendTo("#bar");
}}}
should be written like so:
{{{
  $("#foo").appendTo("#bar");
}}}
in order to avoid losing the bound events.

src/core.js

@@ -238,7 +238,7 @@ jQuery.fn = jQuery.prototype = {
 			var clone = ret.find("*").andSelf();
 
 			this.find("*").andSelf().each(function(i) {
-				var events = this.$events;
+				var events = jQuery.data(this, "events");
 				for ( var type in events )
 					for ( var handler in events[type] )
 						jQuery.event.add(clone[i], type, events[type][handler], events[type][handler].data);
@@ -411,6 +411,8 @@ jQuery.extend = jQuery.fn.extend = function() {
 	return target;
 };
 
+var expando = "jQuery" + (new Date()).getTime(), uuid = 0;
+
 jQuery.extend({
 	noConflict: function(deep) {
 		window.$ = _$;
@@ -451,6 +453,58 @@ jQuery.extend({
 		return elem.nodeName && elem.nodeName.toUpperCase() == name.toUpperCase();
 	},
 	
+	cache: {},
+	
+	data: function( elem, name, data ) {
+		var id = elem[ expando ];
+
+		// Compute a unique ID for the element
+		if ( !id ) 
+			id = elem[ expando ] = ++uuid;
+
+		// Only generate the data cache if we're
+		// trying to access or manipulate it
+		if ( name && !jQuery.cache[ id ] )
+			jQuery.cache[ id ] = {};
+		
+		// Prevent overriding the named cache with undefined values
+		if ( data != undefined )
+			jQuery.cache[ id ][ name ] = data;
+		
+		// Return the named cache data, or the ID for the element	
+		return name ? jQuery.cache[ id ][ name ] : id;
+	},
+	
+	removeData: function( elem, name ) {
+		var id = elem[ expando ];
+
+		// If we want to remove a specific section of the element's data
+		if ( name ) {
+			// Remove the section of cache data
+			delete jQuery.cache[ id ][ name ];
+
+			// If we've removed all the data, remove the element's cache
+			name = "";
+			for ( name in jQuery.cache[ id ] ) break;
+			if ( !name )
+				jQuery.removeData( elem );
+
+		// Otherwise, we want to remove all of the element's data
+		} else {
+			// Clean up the element expando
+			try {
+				delete elem[ expando ];
+			} catch(e){
+				// IE has trouble directly removing the expando
+				// but it's ok with using removeAttribute
+				elem.removeAttribute( expando );
+			}
+
+			// Completely remove the data cache
+			delete jQuery.cache[ id ];
+		}
+	},
+
 	// args is for internal usage only
 	each: function( obj, fn, args ) {
 		if ( args ) {
@@ -836,14 +890,16 @@ jQuery.extend({
 	},
 
 	unique: function(first) {
-		var r = [], num = jQuery.mergeNum++;
+		var r = [], done = {};
 
 		try {
-			for ( var i = 0, fl = first.length; i < fl; i++ )
+			for ( var i = 0, fl = first.length; i < fl; i++ ) {
-				if ( num != first[i].mergeNum ) {
+				var id = jQuery.data(first[i]);
-					first[i].mergeNum = num;
+				if ( !done[id] ) {
+					done[id] = true;
 					r.push(first[i]);
 				}
+			}
 		} catch(e) {
 			r = first;
 		}
@@ -851,8 +907,6 @@ jQuery.extend({
 		return r;
 	},
 
-	mergeNum: 0,
-
 	grep: function(elems, fn, inv) {
 		// If a string is passed in for the function, make a function
 		// for it (a handy shortcut)
@@ -977,10 +1031,15 @@ jQuery.each( {
 		jQuery.className[ jQuery.className.has(this,c) ? "remove" : "add" ](this, c);
 	},
 	remove: function(a){
-		if ( !a || jQuery.filter( a, [this] ).r.length )
+		if ( !a || jQuery.filter( a, [this] ).r.length ) {
+			jQuery.removeData( this );
 			this.parentNode.removeChild( this );
+		}
 	},
 	empty: function() {
+		// Clean up the cache
+		jQuery("*", this).each(function(){ jQuery.removeData(this); });
+
 		while ( this.firstChild )
 			this.removeChild( this.firstChild );
 	}

src/event.js

@@ -41,36 +41,34 @@ jQuery.event = {
 		handler.type = parts[1];
 
 		// Init the element's event structure
-		if (!element.$events)
+		var events = jQuery.data(element, "events") || jQuery.data(element, "events", {});
-			element.$events = {};
 		
-		if (!element.$handle)
+		var handle = jQuery.data(element, "handle", function(){
-			element.$handle = function() {
+			// returned undefined or false
-				// returned undefined or false
+			var val;
-				var val;
-
-				// Handle the second event of a trigger and when
-				// an event is called after a page has unloaded
-				if ( typeof jQuery == "undefined" || jQuery.event.triggered )
-				  return val;
-				
-				val = jQuery.event.handle.apply(element, arguments);
 
+			// Handle the second event of a trigger and when
+			// an event is called after a page has unloaded
+			if ( typeof jQuery == "undefined" || jQuery.event.triggered )
 				return val;
-			};
+			
+			val = jQuery.event.handle.apply(element, arguments);
+			
+			return val;
+		});
 
 		// Get the current list of functions bound to this event
-		var handlers = element.$events[type];
+		var handlers = events[type];
 
 		// Init the event handler queue
 		if (!handlers) {
-			handlers = element.$events[type] = {};	
+			handlers = events[type] = {};	
 			
 			// And bind the global event handler to the element
 			if (element.addEventListener)
-				element.addEventListener(type, element.$handle, false);
+				element.addEventListener(type, handle, false);
 			else
-				element.attachEvent("on" + type, element.$handle);
+				element.attachEvent("on" + type, handle);
 		}
 
 		// Add the function to the element's handler list
@@ -85,7 +83,7 @@ jQuery.event = {
 
 	// Detach an event or set of events from an element
 	remove: function(element, type, handler) {
-		var events = element.$events, ret, index;
+		var events = jQuery.data(element, "events"), ret, index;
 
 		// Namespaced event handlers
 		if ( typeof type == "string" ) {
@@ -111,7 +109,7 @@ jQuery.event = {
 				
 				// remove all handlers for the given type
 				else
-					for ( handler in element.$events[type] )
+					for ( handler in events[type] )
 						// Handle the removal of namespaced events
 						if ( !parts[1] || events[type][handler].type == parts[1] )
 							delete events[type][handler];
@@ -120,9 +118,9 @@ jQuery.event = {
 				for ( ret in events[type] ) break;
 				if ( !ret ) {
 					if (element.removeEventListener)
-						element.removeEventListener(type, element.$handle, false);
+						element.removeEventListener(type, jQuery.data(element, "handle"), false);
 					else
-						element.detachEvent("on" + type, element.$handle);
+						element.detachEvent("on" + type, jQuery.data(element, "handle"));
 					ret = null;
 					delete events[type];
 				}
@@ -130,8 +128,10 @@ jQuery.event = {
 
 			// Remove the expando if it's no longer used
 			for ( ret in events ) break;
-			if ( !ret )
+			if ( !ret ) {
-				element.$handle = element.$events = null;
+				jQuery.removeData( element, "events" );
+				jQuery.removeData( element, "handle" );
+			}
 		}
 	},
 
@@ -156,8 +156,8 @@ jQuery.event = {
 				data.unshift( this.fix({ type: type, target: element }) );
 
 			// Trigger the event
-			if ( jQuery.isFunction( element.$handle ) )
+			if ( jQuery.isFunction( jQuery.data(element, "handle") ) )
-				val = element.$handle.apply( element, data );
+				val = jQuery.data(element, "handle").apply( element, data );
 
 			// Handle triggering native .onfoo handlers
 			if ( !fn && element["on"+type] && element["on"+type].apply( element, data ) === false )
@@ -194,7 +194,7 @@ jQuery.event = {
 		var parts = event.type.split(".");
 		event.type = parts[0];
 
-		var c = this.$events && this.$events[event.type], args = Array.prototype.slice.call( arguments, 1 );
+		var c = jQuery.data(this, "events") && jQuery.data(this, "events")[event.type], args = Array.prototype.slice.call( arguments, 1 );
 		args.unshift( event );
 
 		for ( var j in c ) {

src/selector.js

@@ -140,17 +140,19 @@ jQuery.extend({
 				if ( (m = re.exec(t)) != null ) {
 					r = [];
 
-					var nodeName = m[2], mergeNum = jQuery.mergeNum++;
+					var nodeName = m[2], merge = {};
 					m = m[1];
 
 					for ( var j = 0, rl = ret.length; j < rl; j++ ) {
 						var n = m == "~" || m == "+" ? ret[j].nextSibling : ret[j].firstChild;
 						for ( ; n; n = n.nextSibling )
 							if ( n.nodeType == 1 ) {
-								if ( m == "~" && n.mergeNum == mergeNum ) break;
+								var id = jQuery.data(n);
+
+								if ( m == "~" && merge[id] ) break;
 								
 								if (!nodeName || n.nodeName.toUpperCase() == nodeName.toUpperCase() ) {
-									if ( m == "~" ) n.mergeNum = mergeNum;
+									if ( m == "~" ) merge[id] = true;
 									r.push( n );
 								}
 								
@@ -346,23 +348,23 @@ jQuery.extend({
 
 			// We can get a speed boost by handling nth-child here
 			} else if ( m[1] == ":" && m[2] == "nth-child" ) {
-				var num = jQuery.mergeNum++, tmp = [],
+				var merge = {}, tmp = [],
 					test = /(\d*)n\+?(\d*)/.exec(
 						m[3] == "even" && "2n" || m[3] == "odd" && "2n+1" ||
 						!/\D/.test(m[3]) && "n+" + m[3] || m[3]),
 					first = (test[1] || 1) - 0, last = test[2] - 0;
 
 				for ( var i = 0, rl = r.length; i < rl; i++ ) {
-					var node = r[i], parentNode = node.parentNode;
+					var node = r[i], parentNode = node.parentNode, id = jQuery.data(parentNode);
 
-					if ( num != parentNode.mergeNum ) {
+					if ( !merge[id] ) {
 						var c = 1;
 
 						for ( var n = parentNode.firstChild; n; n = n.nextSibling )
 							if ( n.nodeType == 1 )
 								n.nodeIndex = c++;
 
-						parentNode.mergeNum = num;
+						merge[id] = true;
 					}
 
 					var add = false;

test/data/testrunner.js

@@ -161,7 +161,7 @@ function expect(asserts) {
  * Resets the test setup. Useful for tests that modify the DOM.
  */
 function reset() {
-	document.getElementById('main').innerHTML = _config.fixture;
+	$("#main").html( _config.fixture );
 }
 
 /**

test/unit/event.js

@@ -9,7 +9,7 @@ test("bind()", function() {
 	};
 	$("#firstp").bind("click", {foo: "bar"}, handler).click().unbind("click", handler);
 
-	ok( !$("#firstp").get(0).$events, "Event handler unbound when using data." );
+	ok( !jQuery.data($("#firstp")[0], "events"), "Event handler unbound when using data." );
 	
 	reset();
 	var handler = function(event, data) {
@@ -108,11 +108,11 @@ test("unbind(event)", function() {
 
 	el.click(function() { return; });
 	el.unbind('change',function(){ return; });
-	for (var ret in el[0].$events['click']) break;
+	for (var ret in jQuery.data(el[0], "events")['click']) break;
 	ok( ret, "Extra handlers weren't accidentally removed." );
 
 	el.unbind('click');
-	ok( !el[0].$events, "Removed the events expando after all handlers are unbound." );
+	ok( !jQuery.data(el[0], "events"), "Removed the events expando after all handlers are unbound." );
 });
 
 test("trigger(event, [data], [fn])", function() {