my $mw3= $mw->Button(-text=>"Check brackets",
-command => sub{

my $grammar = q {
startrule: open text close

open: "<"

text: /(.\s)*/

close: ">"
};

my $parser = Parse::RecDescent->new($grammar);

print defined($parser->startrule($mw2->get ("1.0", "500.0")))
? "NO ERROR\n" : "ERROR";
})->pack(-side=>'left');