These are tags that are available for DocBook XML, but we have decided they will not (at this time) be used for KDE Documentation. They are included here for completeness, and so nobody can say “I didn't know I wasn't supposed to use that!”
They fall into two categories: Tags we have definitely decided to not use, in which case we have made a decision to use another tag instead, and tags that are just irrelevant to the documentation we are doing, which you hopefully will never want. Should we write new documentation that can sensibly be marked up with any of these elements, this list will be revised.
If you think you have a use for one of these elements, please, check with the DocBook team first, and be prepared to justify your case.