Return a list of elements which are to be included in the
idindex generated in the backmatter. In principle, this is identical
to (target-element-list), but in practice it
appears to be extremely expensive to do this for the
routine elements, so we here generate a different list
which has those elements removed. In general, we wouldn't much want
to include these in the idindex in any case.
No, just use (target-element-list). Function
(make-idindex) is amazingly slow, but for some
different, unknown, reason than this.
Type: list of strings
List of elements to include in the idindex