Gtk.HTML: type or namespace does not exist in the namespace 'Gtk'

[SjVer]

I've copied the gtk-html sample script but anything html-related doesnt work. The other gtk stuff works just fine but e.g. Gtk.HTMLStream just returns the error that it doesn't exist. What am i missing here?

Code snippet:
Gtk.HTML myhtml; Gtk.HTMLStream mystream = myhtml.Begin("something");

[Jakar510]

For me, neither HTML or HTMLStream could be found.