#!perl
use strict;
use XML::Twig::XPath;
my %record = ();

my $twig= new XML::Twig::XPath( 
twig_handlers => 
  { qr/^Line[1-5]|Author|Publisher|Book|Snap/  => \&line,
    qr/^C\d+/ => \& rating,
  },
);
$twig->parsefile( 'book.xml' );    

sub line {
  my ($t,$e) = @_;
  $record{$e->name} = $e->text;  
  
  if ($e->name eq 'Publisher'){
     report(\%record);
     %record=();
  }
}

sub rating {
  my ($t,$e) = @_;
  my $parent = $e->name.'.';
  for ($e->descendants){
    if ($_->name =~ /[XY]/){
      push @{$record{$parent.$_->name}},$_->text; 
    }    
  }
}

sub report {
  my $hr = shift;
  my @f = qw(Book Snap Line1 Line2 Line3 Line4 Line5);
  my $line = join '|',@$hr{@f};
  for my $key (sort keys %$hr){
    if ($key =~ /^C\d+/){
      print join '|',$line,$key,@{$hr->{$key}};
      print "\n";
    }
  }
}
[download]

Output:

The book of pages||The Beginning|We ceased to exist|Accept it|Now we l
+ive|We reject it|C1.X|10.5|3.5|10.5|10.5|10.5|10.5
The book of pages||The Beginning|We ceased to exist|Accept it|Now we l
+ive|We reject it|C1.Y|11.4|13.4|11.4|11.4|11.4|11.4
...
[download]