In regards to your node title, I had some fun parsing "Hello" using XML::Parser::LiteCopy. Like this:

#!/usr/bin/perl

use strict;
use warnings;
use XML::Parser::LiteCopy;

my $p1 = XML::Parser::LiteCopy->new();
$p1->setHandlers(
    Char  => sub { shift; print "@_\n" },
);
$p1->parse('<foo id="me">Hello</foo>');
[download]

There's an example of how to implement a "Hello, World!" web service here.