#!/usr/bin/perl --
use strict; use warnings;
use XML::Twig;
my $str = <<'EOF';
<NoTe KunG="FoO" ChOp="SuEy">
  <To KunG="FoO">
    <Person KunG="FoO">Satan</Person>
  </To>
  <Beef KunG="FoO"><SaUsAGe KunG="FoO">is Tasty</SaUsAGe></Beef>
</NoTe> 
EOF

{
    my $t = XML::Twig->new(
        pretty_print  => 'indented',
        force_end_tag_handlers_usage => 1,
        start_tag_handlers => {
            _all_ =>  sub {
                $_->set_tag( lc $_->tag );
                if(  $_->has_atts ){
                    my $atts = $_->atts ;
                    $_->set_atts ({
                        map {
                            lc( $_ ) => $atts->{$_}
                        } keys %{ $atts }
                    });
                }
                return
            },
        },
        end_tag_handlers => { _all_ =>  sub { $_->flush; return }, },
    );
    $t->parse($str);
    $t->flush();
}
__END__
<note chop="SuEy" kung="FoO">
  <to kung="FoO">
    <person kung="FoO">Satan</person>
  </to>
  <beef kung="FoO">
    <sausage kung="FoO">is Tasty</sausage>
  </beef>
</note>