Here's a modified version which first checks whether the window manager supports the _NET_WM_STATE_STAYS_ON_TOP atom. 
sub keep_on_top {
    my $w = shift;
    my($wrapper) = $w->toplevel->wrapper;
    eval {
        if (!grep { $_ eq '_NET_WM_STATE_STAYS_ON_TOP' } $w->property(
+'get', '_NET_SUPPORTED', 'root')) {
            die "_NET_WM_STATE_STAYS_ON_TOP not supported";
        }
        $w->property('set', '_NET_WM_STATE', "ATOM", 32,
                     ["_NET_WM_STATE_STAYS_ON_TOP"], $wrapper);
    };
    if ($@) {
        warn $@;
        0;
    } else {
        1;
    }
}

[download]
The code could be expanded to use the <Visibility> or overrideredirect hacks on other window managers.

In reply to Re^2: perlTK always-on-top \ topmost in linux by eserte
in thread perlTK always-on-top \ topmost in linux by Anonymous Monk

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