use XML::Smart ;

my $xml = XML::Smart->new(q`
<nl>
  number list 1
  number list 2
  <ul>
    unnumbered list1 
    unnumbered list 2
    <pl>
      plain list 1
      plain list 2
      <nl>
        numbered list 1
        numbered list 2
      </nl>
    </pl>
  </ul>
</nl>
` , 'html');

my $new_xml = XML::Smart->new() ;

process($xml , $new_xml) ;

print $new_xml->data ;


sub process {
  my $xml = shift ;
  my $new_xml = shift ;
  
  foreach my $node_i ( $xml->nodes ) {
    my @lines = split(/\s*\n\s*/ , $node_i) ;
    
    my $type ;
    if    ( $node_i->key eq 'nl' ) { $type = 'numbered' ;}
    elsif ( $node_i->key eq 'ul' ) { $type = 'unnumbered' ;}
    elsif ( $node_i->key eq 'pl' ) { $type = 'plain' ;}

    my $set_root = 1 if $new_xml->base->null ;

    $new_xml->{list}{type} = $type ;

    $new_xml = $new_xml->{list} if $set_root ;
    
    push( @{$new_xml->{'list-item'}} , @lines) ;
    
    process($node_i , $new_xml->{listitem} ) ;
  }
}