for example, class blchildrenreversed indicates that the user wants to explicitly iterate over elements in reverse order class blchildrenaccountedbylayout indicates that only should children taken into account by layout should be included.
for example, class blchildrenreversed indicates that the user wants to explicitly iterate over elements in reverse order class blchildrenaccountedbylayout indicates that only should children taken into account by layout should be included. | BlChildrenSubset