critical bit (5.2.3.1)

> From section 5.2.3.1:
> Bit 7 of the subpacket type is the "critical" bit.  If set, it
> denotes that the subpacket is one that is critical for the evaluator
> of the signature to recognize.  If a subpacket is encountered that
> is marked critical but is unknown to the evaluating software, the
> evaluator SHOULD consider the signature to be in error.
Can we restrict the SHOULD to hashed subpackets?  Otherwise it is
easy to invalidate a signature by setting the critical bit in a
unhashed subpacket.


  Werner