Only allowed if the group has exactly one group expression. Indicates the following: 1. Groups should be sorted according to the recursive hierarchy (Sort is still used to sort peer groups). 2. Labels (in the document map) should be placed/indented according to the recursive hierarchy. 3. Intra-group show/hide should toggle items according to the recursive hierarchy (see ToggleItem). If filters on the group eliminate a group instance’s parent, it is instead treated as a child of the parent’s parent. In the event of a loop, one of the parent-child relationships will be ignored.
