package SampleClass;

sub new{
    my $class = shift;

    my $self = {};
    $self->{configFile} = shift;
    $self->{fileContents} = ();
    $self->{twig} = new XML::Twig(twig_handlers =>
                                    {
                                     tag => \&tagHandler,
                                     });
    bless $self, $class;
}

. . . 

sub tagHandler{
    my $twig = shift;
    my $tag = shift;
    my $client_name = $tag->first_child('client')->text;
    my $version = $tag->first_child('version')->text;
}