----- Original Message -----
From: "Harald Alvestrand" <harald(_at_)alvestrand(_dot_)no>
Sent: Thursday, September 27, 2001 3:22 AM
Exceptions to MUST NOTs means there are cases which are not prohibited.
The semantics gives me the implication that the appripriate requirement
level is placed between "SHOULD NOT" and "MAY".
MUST NOT means that you never do it, and any implementation that does it is
nonconformant to the spec.
If you find that you have to do it in some case, you have found a bug in
the spec.
Somecases. However, ICMPv6 example case, described in the first mail of this
thread, has not been found but already described in the spec; which is not a
bug at all.
Jiwoong
Note that English is a slippery language, and constructs like "MUST NOT do
X unless Y, Z and W occurs" and its semantic equivalents are quite common.
Most specs have bugs.
Harald