Take a look at the XML::Simple documentation (hint: search for "xml version="), and you'll find:

  XMLDecl => 1  or  XMLDecl => 'string'  *# out - handy*
    If you want the output from "XMLout()" to start with the optional 
+XML
    declaration, simply set the option to '1'. The default XML declara
+tion
    is:

            <?xml version='1.0' standalone='yes'?>

    If you want some other string (for example to declare an encoding
    value), set the value of this option to the complete string you re
+quire.
[download]

That (plus the first couple of lines of the SYNOPSIS) quickly let me arrive at the following code sample, all within a few minutes:

use strict;
use warnings;
use XML::Simple;

my $h_ref = {
    'a' => 1,
    'b' => 2,
    'c' => 3,
    'colors' => [ 'red', 'green', 'blue' ],
    'sub_hash' => {
        'numbers' => [ 0, 1, 2],
        'letters' => {
            'vowels'     => [qw[a e i o u]],
        },
    },
};

my $ref = "1,2,3";
my $xs  = XML::Simple->new(ForceArray => 1, KeepRoot => 1, XMLDecl => 
+1);
my $xml = $xs->XMLout($h_ref);
print "XML is:\n$xml\n";


__END__


[Output]
<?xml version='1.0' standalone='yes'?>
<opt a="1" b="2" c="3">
  <colors>red</colors>
  <colors>green</colors>
  <colors>blue</colors>
  <sub_hash>
    <letters>
      <vowels>a</vowels>
      <vowels>e</vowels>
      <vowels>i</vowels>
      <vowels>o</vowels>
      <vowels>u</vowels>
    </letters>
    <numbers>0</numbers>
    <numbers>1</numbers>
    <numbers>2</numbers>
  </sub_hash>
</opt>
[download]

Update:  Made search string more specific.

Have you tried XMLDecl => '<?xml version="1.0" encoding="UTF-8"?>' ?

Thanks very much. That of course is the piece I was missing.

Regards,

H

Apart from the xdecl, you should also consider installing XML::Parser or the compiled version of XML::SAX. The XML::SAX::PurePerl is slow.