Common usage:
Get items of a first menu level (to display on top of the site), e.g., $result = \Ip\Menu\Helper::getMenuItems('menu1', 1, 1);
Get 7 levels of children of selected page on top menu (to display on a side): $result = \Ip\Menu\Helper::getMenuItems('menu1', 2, 7);
Pass the result to ipSlot('menu', array('items' => $result));
Please note, that items of a child level can only be returned if a selected page is in a breadcrumb parent page.
In opposite case, the function returns an empty array.