In addition to group, there are three group elements: choice, sequence, and all.
The group element groups a set of element declarations so that they can be incorporated into complex type definitions. The group element is limited to the top level of the content model.
The choice element allows one and only one of the elements contained in the group to be present within the containing element.
The sequence element requires the element in the group to appear in the specified sequence within the containing element.
The all element allows the elements in the group to appear (or not appear) in any order in the containing element.