Ron Rosenfeld wrote in
:

So far as the restriction people have been stating having to do with not
being able to use the uncertified GPS units as a substitute for ADF/DME,
that stems from the AIM (1-2-3) (and possibly a change that has not been
published) restricting this type of usage to units that are compliant
with AC90-100.

Ahh... Now I get why I didn't see it.

But the AIM is not regulatory, is it?

If it is, it's a stupid rule. One of the ILSs at my home airport actually
requires an ADF. What a pain.