Nice job zentara, here is a monkey patch

BEGIN {
    package HTML::TagParser::Element;
    sub AUTOLOAD
    {
        my ($name) = our $AUTOLOAD =~ /::(\w+)$/;
        my $method = sub { 
            my $self = shift;
            return $self->subTree->$name( @_ );
        };
        no strict 'refs';
        * { $AUTOLOAD } = $method;
        goto &$method;
    }
}
[download]

Now calling getElementsByClassName on a HTML::TagParser::Element works :)