(aria-*) role and other values

(Bcc to the aria feedback, in case they wish to make a determination
for host languages in general.)

Is it conforming to use a role not currently defined in aria?

For example, aria does not define role="icon", so using it for my own
purposes is not currently barred by the aria spec
(http://www.w3.org/TR/wai-aria/#host_general_role).

I could easily imagine role="icon" being created later -- at which
point my document would become non-conforming.  (Well, unless my own
use was fortuitously equivalent.)

I would expect aria to coordinate with other w3c groups before adding
values, but I would not expect them to coordinate with private usage.

(Of course, an "aria-role" attribute would avoid this problem, by
using aria's own pseudo-namespace.)

-jJ