Please add to documentation as an example.

I wanted the title to be field_company and then field_person_name, separated by "/".
The 1st field is mandatory, the 2nd is sometimes empty.
That's the PHP code I've come up with, to put in the content type's auto-nodetitle definitions tab (when the PHP checkbox is checked).

  $language = $node->language;
  if (!in_array($language, $node->field_company)) $language =  LANGUAGE_NONE;
  $title = $node->field_company[$language][0]['value'];
  $pname = '';
  if (count ($node->field_person_name[$language]) ) :
    $pname = $node->field_person_name[$language][0]['value'];
  if (strlen($pname) > 0):
    return $title . ' / ' . $pname;
    return $title;