It dawned on me, that there is another option which you may be looking for.... the xid option. Some programs, will have the " into an xwindow id " option. It allows you to open a frame in Tk or Gtk2, then get its X window id, then specify that as an option to xterm. See embedding xterm into a Tk app for example.

Here is the simplest example possible. When doing this sort of thing, you may experience glitches in keyboard or mouse focus, but you likely will be lucky.

#!/usr/bin/perl
use strict;
use Tk;

my $mw = MainWindow->new( -bg => 'white' );

$mw->geometry('400x400' . '+100+100');

my $frame1 = $mw->Frame(
    -height => 30,
    -bg     => 'lightblue',
    )->pack( -fill => 'x', -side => 'top' );

my $frame;

my $button = $frame1->Button(
    -text    => 'Open window',
    -command => sub { open_w($frame) },
)->pack;

$frame = $mw->Frame(
    -container => 1,
    -bg        => 'white',
    -relief    => 'sunken',
    -bd        => 2,
)->pack( -fill => 'y', -side => 'left' );

MainLoop();

sub open_w {
    my ($f) = @_;
    my $id = sprintf hex $f->id;
    my $t = $mw->Toplevel( -use => $id );
    system("xterm -into $id &");

}
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