Comment 57 for bug 164640

As been already pointed out, registering in a library is not possible. However if we are going to do it in cairo anyway, in a cairo namespace, then we can forget about registering constants and types and just work with strings. That's whay pango does for pangogravity element for example.

I still think this thing belongs into fontconfig because FreeType exposes this configuration. It's not a cairo-only thing.