Manual:$wgAllowMicrodataAttributes

Details
Allows to enable HTML5 microdata attributes for use in wikitext.

For this to work  must be set to "true", which is the default as well as unchangeable since MW 1.22+.

Starting with 1>phabricator:rMWe789f51f1183d57999926b80c726338d8611e2f1|MW 1.27+ HTML5 microdata attributes will be allowed by default.