Set the behaviour for auto-complete (search-as-you-type) suggestions.
The [https://www.mediawiki.org/wiki/Special:MyLanguage/Extension:CirrusSearch/CompletionSuggester completion suggester] is an algorithm for search suggestions with better typo correction and search relevance. Prefix search is the legacy search-as-you-type suggestion algorithm.
MediaWiki:Cirrussearch-pref-completion-profile-help/en-gb
