but i'm curious to know where you found this information or if just comes from your tries.

Just from tries, its simpler than reading the source

How can i retrieve more infos about tkinit anyway? in the Tk source I just see: It is just a shortcut to call for a MainWindow creation?

Its one of those things monkey see, and yes its just a shortcut , its defined inside Tk.pm, just like MainLoop

 
sub tkinit { return MainWindow->new(@_) }
sub MainLoop
{
 unless ($inMainLoop)
  {
   local $inMainLoop = 1;
   while (Tk::MainWindow->Count)
    {
     DoOneEvent(0);
    }
  }
}
[download]

Anyway I prefere the pryrt's solution ...

Yes, parents kill children, but you don't gotta let the user kill the window so you have to recreate it, just hide/show

#!/usr/bin/perl --
use strict;
use warnings;
use Tk;
my $mw    = MakeMain();
my $phwin = MakePhwin( $mw );
$mw->focus;
$mw->WidgetDump;
MainLoop;

sub MakePhwin {
    my( $mw ) = @_;
    my $phwin = $mw->Toplevel;
    $phwin->protocol( 'WM_DELETE_WINDOW', [sub{shift->withdraw}, $phwi
+n], );
    $phwin->Label(-text => "Close me hit the little x" )->pack;
    return $phwin;
}
sub MakeMain {
    my $mw = tkinit(@_);
    $mw->Button(
        -text => "Restore phwin",
        -command => sub {
            $_->deiconify
                for grep $_->isa('Tk::Toplevel'),
                    $Tk::widget->toplevel->children;
        },
    )->pack;
    $mw->update;
    return $mw;
}
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