Entry family

[evangeli@cnam.fr (Evangelista Sami)]

hello all

what is the meaning of this code which compile well with gnat3.14
under linux:
---------------------------------------------
procedure Test_Index is
   type Id is mod 10;
   protected type Prot is
      entry E (Boolean);
   end Prot;
   protected body Prot is
       entry E (for I in Id) when True is
       begin
          null;
       end;
   end Prot;
   P : Prot;
begin
   P.E(True);
end;
---------------------------------------------why can i declare the
index entry of E as Boolean in the spec and as Id in the body?
Perhaps i didnt understand something about entry index

Thanks for any response