What does raw: do?

I see you used a raw: prefix while transcluding(?) a template in a recent edit to {{head}}. What does it do? I cannot find it anywhere in MediaWiki documentation.

I don't really know what it does, I copied it from {{slink}}.

I've asked the folks at mediawiki.org; hopefully they can enlighten us.

Mark Hershberger posted this explanation: [1].

From what I can tell, the use in {{head}} is actually completely unrelated to its intended use...?