The "true" (old) MediaWiki documentation on search is still on Meta, it needs to be rewritten on mediawiki.org (PD and up to date): https://meta.wikimedia.org/wiki/Help:Searching Nobody reads the help pages, sure. That's why they should be linked from the special pages etc. as some extensions already do. https://bugzilla.wikimedia.org/show_bug.cgi?id=43591
Nemo