Compare
https://www.mediawiki.org/wiki/Special:Version
and
https://www.mediawiki.org/wiki/Special:Version?action=render,
; compare
https://www.mediawiki.org/wiki/Special:Search/badtoken
and
https://www.mediawiki.org/wiki/Special:Search/badtoken?action=render
The visual appearance is the same.
Expected results: no "skin", like https://www.mediawiki.org/wiki/MediaWiki?action=render