I use simplehtmldom (http://sourceforge.net/projects/simplehtmldom/) and the following code to sanitize user input ($ticket_text, removing things like onclick, onkeydown, etc.):

$dom=str_get_html($ticket_text);
foreach ($dom->find('*') as $elem) {
  foreach ($elem->getAllAttributes() as $attr => $val) {
      $elem->removeAttribute($attr);
  }
  if ($elem->hasChildNodes()) {
    foreach ($elem->childNodes as $childNode){
      foreach ($childNode->getAllAttributes() as $attr => $val) {
      $childNode->removeAttribute($attr);
      }
    }
  }
}

Now I receive the following warning in my error_log for the line containing foreach ($elem->childNodes as $childNode){:

WARNING [2] foreach() argument must be of type array|object, bool given

I don’t understand how this can happen. If I do a check with “hasChildNodes()” how can $elem->childNodes yield a boolean?