sub render_via_xml_writer {
    my $doc = shift;
    my $writer = XML::Writer->new(@_);  # extra args go to ->new()
    # my $render_fn;
    # $render_fn = sub {
    sub render_fn {
        my $frag = shift;
        my ($elem, $attrs, $children) = @$frag;
        $writer->startTag( $elem, map {@$_} @$attrs );
        for (@$children) {
            # ref() ? $render_fn->($_) : $writer->characters($_);
            ref() ? render_fn($_) : $writer->characters($_);
        }
        $writer->endTag($elem);
    };
    # $render_fn->($doc);
    render_fn($doc);
    $writer->end();
}