Why was it done this way ?

["Heimlich Manure" <spam@goes.here>]

Hello respectable group,

This may be a silly question but I'm sure there was reasoning behind
allowing such :

with Ada.Text_IO;
use Ada.Text_IO;

procedure My_Example is
    task type T1;
    task type T2;

    task body T1 is
    begin
        Put_Line("Instantiating T2 from T1");
        declare
            T_2_2 : T2;
        begin
            null;
        end;
        end T1;

     task body T2 is
     begin
        Put_Line("Instantiating T1 from T2");
        declare
            T_1_1 : T1;
        begin
            null;
        end;
    end T2;

T_1 : T2;
begin
    null;
end My_Example;

Question is, why is this legit ?