Nope, doesn't.

Sure it does, if you insert it at "break here" it will break -- it still pops up an error dialog (not very useful) but it calls break and breaks :) you should report bug to Tkx author

... Tk isn't.

And then you install Tk

Here's my Tcl/Tk bind/break test. Just keep hitting <tab> and break stops you reaching the second entry. Where and in what form would you specify break in Perl/Tkx to get the second example working. Thank you in anticipation.

_______TCL EG. WORKS WELL______
pack [entry .e1 -textvar v1 -width 50]
set v1 blob
pack [entry .e2 -textvar v2 -width 50]
set v2 blob
proc cb_entry {my_str} { puts -nonewline $my_str; flush stdout}
bind .e1 <KeyPress> {cb_entry $v1; break} ;#<======= break here
bind .e2 <KeyPress> {cb_entry $v2} ;

_______PERL EG. NEEDS BREAK_______
use Tkx;
my $mw;
sub cb_entry {my $win=$_[0]; $mw->g_wm_title("this is $win m8");}

sub main_loop {
my $v1;
my $v2;
$mw = Tkx::widget->new(".");

#WHERE AND HOW TO SPECIFY BREAK IN HERE????        
my $e1 = $mw->new_ttk__entry( -width => 50, 
-textvariable => \$v1, );
$e1->g_pack( -expand => 1, -fill => 'both', );
Tkx::bind($e1, "<Key>", [
    sub { cb_entry($_[0]);   }, Tkx::Ev("%W")
]); 

my $e2 = $mw->new_ttk__entry( -width => 50, 
-textvariable => \$v2, );
$e2->g_pack( -expand => 1, -fill => 'both', );
Tkx::bind($e2, "<Key>", [
    sub { cb_entry($_[0]);  }, Tkx::Ev("%W")
]);
     
    Tkx::MainLoop(); 
}

main_loop;
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use it anywhere you want, Tkx::break(), and then suffer the popup bug (its a bug)