# if you don't care where in the structure is the tag, this would be sufficient:

use strict;
use warnings;

use XML::Rules;

my $parser = XML::Rules->new(
    namespaces => {
        'http://schemas.xmlsoap.org/soap/envelope/' => 'soap',
        'http://com/Server' => 'srv',
        'http://com' => 'com'
    },
    rules => {
        'srv:MaxCode' => sub {
            my ($attrs, $parser) = @_[1,4];
            $parser->return_this($attrs->{_content});
        }
    }
);

my $content = qq|<?xml version=\'1.0\' encoding=\'UTF-8\'?><soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
 <soap:Header><ais:requestID xmlns:ais="http://com">
  {7f000001-47db2420000001569783cdb88136}
  </ais:requestID>
  </soap:Header>
  <soap:Body>
  <soap:Fault>
  <faultcode>soap:Server</faultcode>
  <faultstring>
    check expression:
  </faultstring>
  <faultactor>CheckTwo</faultactor>
  <detail>
   <longDescription xmlns="http://com">
    Exception occurred
   </longDescription>
<MaxCode xmlns="http://com/Server">-2225</MaxCode>
</detail>
</soap:Fault>
</soap:Body>
</soap:Envelope>|;



my $result = $parser->parse($content);

print $result;