The source code

    /**
     * @ignore
     * delegate events for children
     * @author yiminghe@gmail.com
     */
    KISSY.add("component/base/delegate-children", function (S, Event) {

        var UA = S.UA,
            ie = S.Env.host.document.documentMode || UA.ie,
            Features = S.Features,
            Gesture = Event.Gesture,
            isTouchSupported = Features.isTouchSupported();

        function DelegateChildren() {
        }

        function handleChildMouseEvents(e) {
            if (!this.get("disabled")) {
                var control = this.getOwnerControl(e.target, e);
                if (control && !control.get("disabled")) {
                    // Child control identified; forward the event.
                    switch (e.type) {
                        case Gesture.start:
                            control.handleMouseDown(e);
                            break;
                        case Gesture.end:
                            control.handleMouseUp(e);
                            break;
                        case Gesture.tap:
                            control.performActionInternal(e);
                            break;
                        case "mouseover":
                            control.handleMouseOver(e);
                            break;
                        case "mouseout":
                            control.handleMouseOut(e);
                            break;
                        case "contextmenu":
                            control.handleContextMenu(e);
                            break;
                        case "dblclick":
                            control.handleDblClick(e);
                            break;
                        default:
                            S.error(e.type + " unhandled!");
                    }
                }
            }
        }

        DelegateChildren.ATTRS = {
            delegateChildren: {
                value: true
            }
        };

        S.augment(DelegateChildren, {

            __bindUI: function () {
                var self = this,
                    events;
                if (self.get("delegateChildren")) {

                    events = Gesture.start + " " + Gesture.end + " " + Gesture.tap + " ";

                    if (!isTouchSupported) {
                        events += "mouseover mouseout contextmenu " +
                            (ie && ie < 9 ? "dblclick " : "");
                    }

                    self.get("el").on(events, handleChildMouseEvents, self);
                }
            },

            /**
             * Get child component which contains current event target node.
             * @protected
             * @member KISSY.Component.Container
             * @param {HTMLElement} target Current event target node.
             * @return {KISSY.Component.Controller}
             */
            getOwnerControl: function (target) {
                var self = this,
                    children = self.get("children"),
                    len = children.length,
                    elem = self.get("el")[0];
                while (target && target !== elem) {
                    for (var i = 0; i < len; i++) {
                        if (children[i].get("el")[0] === target) {
                            return children[i];
                        }
                    }
                    target = target.parentNode;
                }
                return null;
            }
        });

        return DelegateChildren;
    }, {
        requires: ['event']
    });