Board Thread:Support Requests - Getting Technical/@comment-4828844-20170805070841/@comment-32354545-20170805071729

is the syntax for the old, really old method of collapsing tables, which relied on custom JavaScript (which can be found in c:hunterxhunter:Mediawiki:Common.js).

It's unsupported now and pretty much entirely replaced with a new system requiring no custom JavaScript. You can update to the new system with  such as seen in this edit.

Take a look at http://hunterxhunter.wikia.com/index.php?title=Special%3AAllPages&from=Nav&to=Nb&namespace=10 because there seem to be a few navboxes using this old code, most of which are protected. After updating them, you could remove the code from Common.js.