Ability to avoid expando collisions

src/core.js

@@ -372,12 +372,20 @@ jQuery.extend = jQuery.fn.extend = function() {
 };
 
 jQuery.extend({
-	noConflict: function( deep ) {
+	noConflict: function( deep, expandoPrefix ) {
 		window.$ = _$;
 
 		if ( deep ) {
 			window.jQuery = _jQuery;
 		}
+
+                // If the expando needs a prefix for explicit uniqueness
+                // and the cache has not been used yet (otherwise it's worth the risk).
+                // See #6842
+                if ( expandoPrefix && jQuery.isEmptyObject( jQuery.cache ) ) {
+                        // Set the expando to the old one plus the prefix
+                        jQuery.expando = expandoPrefix + jQuery.expando;
+                }
 
 		return jQuery;
 	},

src/data.js

@@ -9,8 +9,9 @@ jQuery.extend({
 	// Please use with caution
 	uuid: 0,
 
-	// Unique for each copy of jQuery on the page	
-	expando: "jQuery" + jQuery.now(),
+	// Usually unique for each copy of jQuery on the page and for each version
+	// Use a jQuery.noConflict(true, 'unqiuePrefix') to manually avoid time collisions
+	expando: "jQuery" + jQuery.fn.jquery + jQuery.now(),
 
 	// The following elements throw uncatchable exceptions if you
 	// attempt to add expando properties to them.

test/unit/core.js

@@ -183,7 +183,7 @@ test("browser", function() {
 }
 
 test("noConflict", function() {
-	expect(7);
+	expect(9);
 
 	var $$ = jQuery;
 
@@ -197,8 +197,32 @@ test("noConflict", function() {
 	equals( jQuery, originaljQuery, "Make sure jQuery was reverted." );
 	equals( $, original$, "Make sure $ was reverted." );
 	ok( $$("#main").html("test"), "Make sure that jQuery still works." );
-
-	jQuery = $$;
+
+	jQuery = $ = $$;
+
+	var oldExpando = jQuery.expando;
+	var oldCache   = jQuery.cache;
+	var testPrefix = 'testPrefix';
+
+	// simulate no data in the cache
+	jQuery.cache = {};
+
+	equals( jQuery.noConflict(true, testPrefix).expando, testPrefix + oldExpando, "noConflict prefix was added" );
+
+	jQuery = $ = $$;
+
+	// Set the expando back to the original
+	jQuery.expando = oldExpando;
+
+	// Populate jQuery.cache
+	jQuery.cache = {'key': 'val'};
+
+	equals( jQuery.noConflict(true, testPrefix).expando, oldExpando, "noConflict does not allow a prefix if jQuery.cache has been used" )
+
+	jQuery = $ = $$;
+
+	// Replace the data that was there prior to the tests for good measure
+	jQuery.cache = oldCache;
 });
 
 test("trim", function() {