Ada 95 and Class attribute for none-tagged incomplete type

["Hibou57 (Yannick Duchêne)" <yannick_duchene@yahoo.fr>]

Hello,

I've learned something mostly surprising today : in Ada 95, this was
allowed to use the Class attribute with a prefix which was an
incomplete type.... even not tagged.

I've learned about it here :

http://www.adaic.org/standards/05rat/html/Rat-1-3-3.html
>> ------------------
The introduction of tagged incomplete types clarifies the ability to
write
type T_Ptr is access all T'Class;
This was allowed in Ada 95 even though we had not declared T as tagged
at this point. Of course it implied that T would be tagged. In Ada
2005 this is frowned upon since we should now declare that T is tagged
incomplete if we wish to declare a class wide access type. For
compatibility the old feature has been retained but banished to Annex
J for obsolescent features.
>> ------------------

The part of the mentionned annex J
>> ------------------
For the first subtype S of a type T declared by an
incomplete_type_declaration that is not tagged, the following
attribute is defined:
S'Class
Denotes the first subtype of the incomplete class-wide type rooted at
T. The completion of T shall declare a tagged type. Such an attribute
reference shall occur in the same library unit as the
incomplete_type_declaration.
>> ------------------

But why was it allowed ?
There was no way to declare an incomplete tagged ?
So why to allow reference to a Class attribute in such circumstances ?

This seems weird ... to allow to make reference to a class attribute
of a none-tagged type (even if the complete view is tagged)

Was this a design error or were there some reasons or is there
something I did not understand ?