Board Thread:Support Requests - Getting Technical/@comment-14779707-20130823125813/@comment-3147293-20130824122243

This is because Wikipedia is keeping the old script as a fallback for editors who still are using it. If you really wanna use the same code as theirs, you have to visit Wikipedia's MediaWiki:Common.js page, copy the section named Collapsible Table function and put it into your site's MediaWiki:Common.js.

However, there are some benefits of using  since this new method doesn't require any JS setup (as I described before), furthermore, both MediaWiki and Wikia is in charge of its maintenance, whereas the old one is pretty deprecated now.

That being said, if you're gonna go for this one, you just have to replace  with   and it will start to work. Also, I suggest you to take a look on Help:Collapsing. That short help page contains nearly every information about collapsible elements.