terminal filter matches the currentposition if the current position is a terminal position position, which means it has no children.
By default, CQL considers only mainline positions, when there is only one terminal position. However, if
variations is set in the CQL header, then there may be multiple terminal positions, as the last position of each variation is a terminal position.
terminal is equivalent to the filter
not child , since a position is terminal if and only if it has no child.