I want to automate changing some settings in an app which uses XML config files, but I am not an XML expert and don't have real experience with any of the XML modules (other than knowing from reading here that I need to avoid XML::Simple). I like starting from "known good" code as examples, and playing around until I understand it better. I found some of haukex's examples with XML::Rules, especially Re^6: XML compare with a key and Re: How do I get a list in a perl hash generated from an XML?, which got me to the point that I could get the XML parsed into an initial data structure which seems reasonable to me.

But my next goal was to round-trip the config file: to see if I could get an output file that's compatible with the input, so it's still usable as a config file for the app. So far, I've got a short example of:

#!perl

use 5.012; # strict, //
use warnings;
use Data::Dump;
use XML::Rules;

my $xml_doc = <<EOXML;
<?xml version="1.0" encoding="UTF-8" ?>
<!-- important instructions to manual editors -->
<root>
    <group name="blah">
        <!-- important instructions for group "blah" -->
        <tag/>
    </group>
    <group name="second">
        <!-- important instructions for group "second" -->
        <differentTag/>
    </group>
</root>
EOXML

my $parser = XML::Rules->new(
    stripspaces => 3|4,
    rules => [
        _default => 'raw',
    ],
);

#dd
my $data = $parser->parse($xml_doc);

print
my $out = $parser->ToXML($data, 0, "  ", "") . "\n";

__DATA__

<root>
  <group name="blah">
    <tag/>
  </group>
  <group name="second">
    <differentTag/>
  </group>
</root>
[download]

... But there are two things I haven't figured out how to do, as evidenced by the differences between the input text and the output text.

• How do I keep the <?xml ...?> prolog? That is, if the original XML tells me it's encoding="UTF-8" or encoding="Windows-1252", I want to be able to preserve that in my XML output. I searched XML::Rules for <?xml or prolog and couldn't find anything. So is it possible to have XML::Rules include that during its parsing?
• Is it possible to maintain comments, and their relationship to the existing tags? I searched for comment or <!--, but again couldn't find anything. This is important, because as the dummy data shows, the comments are important instructions to the user who is manually editing the config file, and I don't want to lose that information as I round-trip through my perl-based config-file editor.

So, is XML::Rules the right choice for this? (And if so, how do I accomplish it?) If not, which module is better equipped for my goals? (And could you provide a similar example, showing how to round-trip through the data structure and still have prolog and comments?)

Thank you.

edit: fixed missing sentence separator and missing paragraph indicators; fix title

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