$main_self->{txt_box}=txt_box->new( $main_self->{frm}, sub {$main_self->updt} );

...

sub new {  my $class = shift;  my $new_self = {}; bless( $new_self, $class ); #std line
    $new_self->{parent_widg}=shift;
    $new_self->{sub_to_call_on_keypress}=shift;   <===================LOOK HERE
    $new_self->{contents}='';
    $new_self->{entry}=$new_self->{parent_widg}->new_ttk__entry( -width => 50, -textvariable => \$new_self->{contents}, );
    $new_self->{entry}->g_pack( -expand => 0, -fill => 'x',  -side => top);   #-fill => 'both'
    globals::new_bindtag('new_tag',$new_self->{entry},4); 
    Tkx::bind( 'new_tag', "<Key>", [ sub { $new_self->upon_keypress(@_) }, Tkx::Ev("%W","%K","%k") ] );
    return $new_self;  } #std line

sub upon_keypress { #calls the sub/method you supplied...if an ordinary sub you supply \&sub_nm if method then just obj->method_nm
    my ($new_self, $win, $key_nm, $key_no) = @_; #tick
    print "in upon_keypress and so far you've got $new_self->{contents}\n "; #tick
    $new_self->{sub_to_call_on_keypress}->( $new_self->{contents}  ); #bug here...$self->{contents} gets passed to ORDINARY SUB but not updt method    <===================LOOK HERE
}