draft-ietf-sieve-mime-loop: meaning of :anychild when :mime is not

Tim Polk pointed out during the IESG review that the behavior of 
:anychild without :mime is not defined.
In a private exchange Tony listed alternatives

   1)    The ":anychild" tagged argument is used with the ":mime" tagged
   argument to modify its behavior.
or
   2)    The ":anychild" tagged argument is used with the ":mime" tagged
   argument to modify its behavior. The ":anychild" tagged argument
   is not used without the ":mime" tagged argument.
or
   3)    The ":anychild" tagged argument may only be used with the
   ":mime" tagged argument to modify its behavior.

and mentioned that he slightly prefers 1). Cyrus expressed his 
preference for option 3). I think we need to get WG consensus on this 
change.