+ /**
+ * A single item may alias a set of items, by having dependencies,
+ * but no source. Queuing the item queues the dependencies.
+ *
+ * Example: The extending class WP_Scripts is used to register 'scriptaculous' as a set of registered handles:
+ * <code>add( 'scriptaculous', false, array( 'scriptaculous-dragdrop', 'scriptaculous-slider', 'scriptaculous-controls' ) );</code>
+ *
+ * The src property is false.
+ **/
+ if ( ! $this->registered[$handle]->src ) {