---------------------------------- Event handlers 
Inserts the splitter for a given region. A reference to the splitter is also stored
on the component as "splitter".
@private
function (item, index, hidden) {
        var region = item.region,
            splitter = {
                xtype: 'bordersplitter',
                collapseTarget: item,
                id: item.id + '-splitter',
                hidden: hidden,
                canResize: item.splitterResize !== false
            },
            at = index + ((region == 'south' || region == 'east') ? 0 : 1);

        // remove the default fixed width or height depending on orientation:
        if (item.isHorz) {
            splitter.height = null;
        } else {
            splitter.width = null;
        }

        if (item.collapseMode == 'mini') {
            splitter.collapsedCls = item.collapsedCls;
        }

        item.splitter = this.owner.add(at, splitter);
    }