use strict;
use XML::Twig;

my @nodes = qw(title toc bar);

my %found;
my $t = XML::Twig->new(
    twig_handlers => { map { $_ => sub { $found{$_->name()}++ }; } @nodes }
);

$t->parsefile(shift()); # read file specified at command line

$t->flush; # update: you may need this

for (@nodes) {
    die "$_ not found" unless $found{$_};
}