Board Thread:Support Requests - Designing Your Wiki/@comment-5095122-20130502224432/@comment-10688548-20130502225132

Newer versions of Mediawiki will intelligently collapse themselves if you append  to them.

There was an old system relying on Javascript, in which you appended. Since Mediawiki now supports it out-of-the-box, it's obsolete.

Help:Collapsing might help.