Manual:$wgHtml5

This setting was not removed in MW 1.22+ but starting with this branch setting it to "false" has no longer any impact.

Details
Whether to output an HTML5 doctype. See HTML5 for more information.

If  is set to "true", the markup will be constructed so it can still be processed as XML.

In order to allow the use of microdata attributes in wikitext, set  to "true".