Email from Brad Pierce dated 
Although
I agree with the motivation for EN-33, I would like to propose a different
solution
(in Syntax 3-1, Syntax 3-3, Section A.2.2.1)
 
 enum_name_declaration ::=
   
enum_identifier [ [ integral_number [ : integral_number
] ] ] [ = constant_expression ]
 
--
Brad
 
p.s.  EN-6 is good.