###
### walk_html
###

## Chapter 1 section 7

sub walk_html {
  my ($html, $textfunc, $elementfunc) = @_;
  return $textfunc->($html) unless ref $html;   # It's a plain string

  my @results;
  for my $item (@{$html->{_content}}) {
    push @results, walk_html($item, $textfunc, $elementfunc);
  }
  return $elementfunc->($html, @results);
}