Protected types and visibility of their internals

[Maciej Sobczak <see.my.homepage@gmail.com>]

Consider a protected type in some package:

package P is
   protected type PT is
      procedure Foo;
   private
      X : Some_Type;
   end PT;
end P;

The protected type has a component X of Some_Type, which is entirely
the private business of the protected type.

Where this type should be declared?

My first natural attempt was to put the declaration of Some_Type in
the private part of PT, but this seems to be impossible even at the
grammar level.
My second, although less natural attempt was to put it to the private
part of P, but then it is not visible to PT.

The only place that seems to be allowed is the visible part of P. I
don't find it very comfortable, because I do not intend the users of P
to see Some_Type.
What is the rationale for this?
Can you recommend some other solution that enforces strict coding
practice?

--
Maciej Sobczak * www.msobczak.com * www.inspirel.com