test3.pp

class first {
  tag('doot')
}

class second {
  if tagged(first) {
    warning('first tag found')
  } else {
    warning('first tag not found')
  }
  if tagged(doot) {
    warning('doot tag found')
  } else {
    warning('doot tag not found')
  }
  if tagged(third) {
    warning('third tag found')
  } else {
    warning('third tag not found')
  }
}

class third {
}

class {
  'first':;
  'second':;
  'third':;
}

Class['first'] -> Class['second'] <- Class['third']