#!/usr/bin/perl --
use strict; use warnings;
use XML::Rules;
use Data::Dump qw/ dd /;

my $wanted = <<'__XML__';
<?xml version="1.0" encoding="utf-8"?>
<opt>
  <key0>
    <devices>
      <dev0>
        <param id="name">joe</param>
        <param id="type">user</param>
      </dev0>
    </devices>
  </key0>
  <key1>
    <devices>
      <dev0>
        <param id="name">mary</param>
        <param id="type">user</param>
      </dev0>
    </devices>
  </key1>
</opt>
__XML__



use XML::Rules;
my $t = XML::Rules->new(
    qw/ stripspaces 8 /,
    rules => {
      'dev0,devices,key0,key1,opt' => 'no content',
      'param' => 'as array',
    },
);

my $XmlRef  = $t->parse( $wanted );
dd $XmlRef;
print $t->toXML( opt => $XmlRef->{opt}, undef, "  ", );
__END__
{
  opt => {
           key0 => {
                     devices => {
                       dev0 => {
                         param => [
                           { _content => "joe", id => "name" },
                           { _content => "user", id => "type" },
                         ],
                       },
                     },
                   },
           key1 => {
                     devices => {
                       dev0 => {
                         param => [
                           { _content => "mary", id => "name" },
                           { _content => "user", id => "type" },
                         ],
                       },
                     },
                   },
         },
}
<opt>
  <key0>
    <devices>
      <dev0>
        <param id="name">joe</param>
        <param id="type">user</param>
      </dev0>
    </devices>
  </key0>
  <key1>
    <devices>
      <dev0>
        <param id="name">mary</param>
        <param id="type">user</param>
      </dev0>
    </devices>
  </key1>
</opt>