Seeing that some sandbox pages have categories that should only appear on main space articles, I was thinking of using a bot to put them inside "nowiki" or "comment" tags, but someone on the French community talk page had the idea to let MediWiki do the work.
In fact, it would be better if MediaWiki could recognise if a category is part of the "category:main space" or "category:non-main space" and display it only if the page is in the main space or not.
As the problem occurs in all Wikipedias, and even in all wikis, I wonder if it is possible that MediaWiki do that.
I created a task on phabricator, but I don't know if I did right : https://phabricator.wikimedia.org/T125855
Regards, ~~~~