YUI: DragDrop inside scrolled parent

This is a prototype of DragDrop running inside a scrolled parent.

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The Javascript

(function() {
    var Dom = YAHOO.util.Dom,
        Event = YAHOO.util.Event;

if (y < this.lastY) { 
                    this.goingUp = true; 
                } else if (y > this.lastY) { 
                    this.goingUp = false; 
                }

this.lastY = y;

var pageY = Event.getPageY(ev),
                    ch = this.getEl().clientHeight,
                    scrollTop = false;

this.scrollBy =  ((ch * 2) + this.overFlow);

if (this.goingUp) {
                    var deltaTop = this.xy[1] + (ch + this.overFlow);
                    if (pageY < deltaTop) {
                        scrollTop = this.scrollParent.scrollTop - this.scrollBy;
                    }
                } else {
                    var deltaBottom = this.clientHeight + this.xy[1] - (ch + this.overFlow);
                    if ((pageY > deltaBottom)) {
                        scrollTop = this.scrollParent.scrollTop + this.scrollBy;
                    }
                }
                this.scrollTo(scrollTop);
            },
            scrollTo: function(scrollTop) {
                this.currentScrollTop = scrollTop;
                if (this.scrollInt) {
                    clearInterval(this.scrollInt);
                }
                if (scrollTop) {
                    var self = this;
                    this.scrollInt = setInterval(function() {
                        if ((self.currentScrollTop < 0) || (self.currentScrollTop > self.scrollHeight)) {
                            clearInterval(self.scrollInt);
                        }
                        self.scrollParent.scrollTop = self.currentScrollTop;
                        YAHOO.util.DragDropMgr.refreshCache();
                        if (self.goingUp) {
                            self.currentScrollTop = self.currentScrollTop - self.scrollBy;
                        } else {
                            self.currentScrollTop = self.currentScrollTop + self.scrollBy;
                        }
                    }, 10);
                }
            },
            onDragDrop: function() {
                Dom.removeClass(this.dragger, 'dragging');
                if (this.scrollInt) {
                    clearInterval(this.scrollInt);
                }
            },
            endDrag: function() {
                Dom.removeClass(this.dragger, 'dragging');
                this.dragger.style.position = '';
                this.dragger.style.top = '';
                this.dragger.style.left = '';
                if (this.scrollInt) {
                    clearInterval(this.scrollInt);
                }
            }
        });

var lis = Dom.get('demo').getElementsByTagName('li');
        for (var i = 0; i < lis.length; i++) {
            new YAHOO.util.DDTarget(lis[i]);
        }

Event.on('demo', 'mousedown', function(ev) {
            var tar = Event.getTarget(ev);
            if (tar.tagName.toLowerCase() == 'li') {
                Dom.addClass(tar, 'dragging');
                var dd = new scroll(tar, '', { scroll: 'demo' });
                dd.handleMouseDown(ev);
                dd.dragger = tar;
            }
        });

})();