Extension:MixedNamespaceSearchSuggestions

MixedNamespaceSearchSuggestions makes the search box man>Special:MyLanguage/Manual:$wgEnableOpenSearchSuggest|autocomplete terms matching page names from content namespaces in addition to full page names.

The help>Special:MyLanguage/Help:Namespaces|namespace name is stripped from each title and shown in a byline next to it.

The extension was originally thought for wikis having many similar namespaces, where the user can't be expected to be able to prefix the correct namespace when searching for a title.  is ignored.