Returns the item that is currently active inside this TabPanel.
@return {Ext.Component} The currently active item.
function() {
        var me = this,
            // Ensure the calculated result references a Component
            result = me.getComponent(me.activeTab);

        // Sanitize the result in case the active tab is no longer there.
        if (result && me.items.indexOf(result) != -1) {
            me.activeTab = result;
        } else {
            me.activeTab = null;
        }

        return me.activeTab;
    }