sub reduce {
  my ($ref) = @_;

  if (ref($ref) eq 'REF') {       # recurse into references...
    $$ref = reduce($$ref);
  } elsif (UNIVERSAL::isa($ref, 'HASH')) {
    my @keys = keys %$ref;
    if (scalar (@keys) == 0) {    # empty hash becomes an empty string
      return '';
    } elsif (scalar (@keys) == 1 && $keys[0] eq 'content') {
      $ref = $ref->{$keys[0]};    # 'content'-only becomes the value
    } else {
      foreach (keys %$ref) {      # recurse into multi-element hashes
        $ref->{$_} = reduce($ref->{$_});
      }
    }
  } elsif (UNIVERSAL::isa($ref, 'ARRAY')) {
    foreach (@$ref) {             # recurse into arrays
      reduce($_);
    }
  }
  return $ref;
}