As alternative to XML::Rules, there also is XML::Twig, which basically is the same but a little different. It requires XML::Parser as prerequisite.

If you want to see all the Xpath expressions that occur in an XML file, here's a program I use to find the structure of an XML file in absence of an XSD:

#!perl
use strict;
use XML::Twig;

my %path;

sub handle_tag {
    my( $twig )= @_;
    my $tag= $_;
    my $path= $tag->path( );
    print $path, "\n"
        unless $path{ $path }++;
    $tag->purge;
};

  my $twig=XML::Twig->new(   
    twig_handlers => 
      {
           _all_ => \&handle_tag,
      },
);

$twig->parsefile( $ARGV[0] );

print "\n-------\n\n";

for my $k (sort keys %path) {
    print "$k\t$path{ $k }\n";
};
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