The source code

    Ext.ux.Portal = Ext.extend(Ext.Panel, {
        layout : 'column',
        autoScroll : true,
        cls : 'x-portal',
        defaultType : 'portalcolumn',

        initComponent : function(){
            Ext.ux.Portal.superclass.initComponent.call(this);
            this.addEvents({
                validatedrop:true,
                beforedragover:true,
                dragover:true,
                beforedrop:true,
                drop:true
            });
        },

        initEvents : function(){
            Ext.ux.Portal.superclass.initEvents.call(this);
            this.dd = new Ext.ux.Portal.DropZone(this, this.dropConfig);
        },

        beforeDestroy : function() {
            if(this.dd){
                this.dd.unreg();
            }
            Ext.ux.Portal.superclass.beforeDestroy.call(this);
        }
    });

    Ext.reg('portal', Ext.ux.Portal);

    Ext.ux.Portal.DropZone = function(portal, cfg){
        this.portal = portal;
        Ext.dd.ScrollManager.register(portal.body);
        Ext.ux.Portal.DropZone.superclass.constructor.call(this, portal.bwrap.dom, cfg);
        portal.body.ddScrollConfig = this.ddScrollConfig;
    };

    Ext.extend(Ext.ux.Portal.DropZone, Ext.dd.DropTarget, {
        ddScrollConfig : {
            vthresh: 50,
            hthresh: -1,
            animate: true,
            increment: 200
        },

        createEvent : function(dd, e, data, col, c, pos){
            return {
                portal: this.portal,
                panel: data.panel,
                columnIndex: col,
                column: c,
                position: pos,
                data: data,
                source: dd,
                rawEvent: e,
                status: this.dropAllowed
            };
        },

        notifyOver : function(dd, e, data){
            var xy = e.getXY(), portal = this.portal, px = dd.proxy;

            // case column widths
            if(!this.grid){
                this.grid = this.getGrid();
            }

            // handle case scroll where scrollbars appear during drag
            var cw = portal.body.dom.clientWidth;
            if(!this.lastCW){
                this.lastCW = cw;
            }else if(this.lastCW != cw){
                this.lastCW = cw;
                portal.doLayout();
                this.grid = this.getGrid();
            }

            // determine column
            var col = 0, xs = this.grid.columnX, cmatch = false;
            for(var len = xs.length; col < len; col++){
                if(xy[0] < (xs[col].x + xs[col].w)){
                    cmatch = true;
                    break;
                }
            }
            // no match, fix last index
            if(!cmatch){
                col--;
            }

            // find insert position
            var p, match = false, pos = 0,
                c = portal.items.itemAt(col),
                items = c.items.items, overSelf = false;

            for(var len = items.length; pos < len; pos++){
                p = items[pos];
                var h = p.el.getHeight();
                if(h === 0){
                    overSelf = true;
                }
                else if((p.el.getY()+(h/2)) > xy[1]){
                    match = true;
                    break;
                }
            }

            pos = (match && p ? pos : c.items.getCount()) + (overSelf ? -1 : 0);
            var overEvent = this.createEvent(dd, e, data, col, c, pos);

            if(portal.fireEvent('validatedrop', overEvent) !== false &&
               portal.fireEvent('beforedragover', overEvent) !== false){

                // make sure proxy width is fluid
                px.getProxy().setWidth('auto');

                if(p){
                    px.moveProxy(p.el.dom.parentNode, match ? p.el.dom : null);
                }else{
                    px.moveProxy(c.el.dom, null);
                }

                this.lastPos = {c: c, col: col, p: overSelf || (match && p) ? pos : false};
                this.scrollPos = portal.body.getScroll();

                portal.fireEvent('dragover', overEvent);

                return overEvent.status;
            }else{
                return overEvent.status;
            }

        },

        notifyOut : function(){
            delete this.grid;
        },

        notifyDrop : function(dd, e, data){
            delete this.grid;
            if(!this.lastPos){
                return;
            }
            var c = this.lastPos.c, col = this.lastPos.col, pos = this.lastPos.p;

            var dropEvent = this.createEvent(dd, e, data, col, c,
                pos !== false ? pos : c.items.getCount());

            if(this.portal.fireEvent('validatedrop', dropEvent) !== false &&
               this.portal.fireEvent('beforedrop', dropEvent) !== false){

                dd.proxy.getProxy().remove();
                dd.panel.el.dom.parentNode.removeChild(dd.panel.el.dom);

                if(pos !== false){
                    if(c == dd.panel.ownerCt && (c.items.items.indexOf(dd.panel) <= pos)){
                        pos++;
                    }
                    c.insert(pos, dd.panel);
                }else{
                    c.add(dd.panel);
                }

                c.doLayout();

                this.portal.fireEvent('drop', dropEvent);

                // scroll position is lost on drop, fix it
                var st = this.scrollPos.top;
                if(st){
                    var d = this.portal.body.dom;
                    setTimeout(function(){
                        d.scrollTop = st;
                    }, 10);
                }

            }
            delete this.lastPos;
        },

        // internal cache of body and column coords
        getGrid : function(){
            var box = this.portal.bwrap.getBox();
            box.columnX = [];
            this.portal.items.each(function(c){
                 box.columnX.push({x: c.el.getX(), w: c.el.getWidth()});
            });
            return box;
        },

        // unregister the dropzone from ScrollManager
        unreg: function() {
            //Ext.dd.ScrollManager.unregister(this.portal.body);
            Ext.ux.Portal.DropZone.superclass.unreg.call(this);
        }
    });