lib/collection/item-group.js
function forEachItemGroup (callback) {
        this.items.each(function (item) {
            if (ItemGroup.isItemGroup(item)) {
                item.forEachItemGroup(callback);
                callback(item, this); // eslint-disable-line callback-return
            }
        }, this);
    }
function forEachItemGroup (callback) {
        this.items.each(function (item) {
            if (ItemGroup.isItemGroup(item)) {
                item.forEachItemGroup(callback);
                callback(item, this); // eslint-disable-line callback-return
            }
        }, this);
    }
function forEachItemGroup ( callback ) { this . items . each ( function ( item ) { if ( ItemGroup . isItemGroup ( item ) ) { item . forEachItemGroup ( callback ) ; callback ( item , this ) ; // eslint-disable-line callback-return } } , this ) ; }
Calls the callback for each itemgroup belonging to itself. All ItemGroups encountered will also,
call the callback on their own ItemGroups

@private
@param {Function} callback
Calls the callback for each itemgroup belonging to itself . All ItemGroups encountered will also call the callback on their own ItemGroups