use XML::Twig;
use IO::Handle;

my $stdin = IO::Handle->new();
$stdin->fdopen(fileno(STDIN),"r") or die "fdopen STDIN: $!";

XML::Twig->new(
  twig_handlers => { 's' => \&process_sentence }
)->safe_parse($stdin);

sub process_section {
  my( $t, $elem) = @_;
  ...
  $elem->purge;  # don't want to print the original text 
}