use strict;
use XML::Rules;

my $string = qq~<?xml version="1.0"?>
<ItemLookupResponse xmlns="http://webservices.amazon.com/AWSECommerceService/2013-08-01">
  <Items>
    <Item>
      <ASIN>B01KI4JSQY</ASIN>
    </Item>
  </Items>
</ItemLookupResponse>
~;

my $parser = XML::Rules->new(
    rules => {
        ASIN => [
            '/ItemLookupResponse/Items/Item' => sub { print "ASIN: $_[1]->{_content}\n"; },
            sub { print "ASIN at an unexpected place\n"; }
        ]
    },
    xmlns => {
        'http://webservices.amazon.com/AWSECommerceService/2013-08-01' => ''
    }
);
$parser->parse($string);