code: protected function getPublicNameFromIndex($subject)
      {
          foreach ($this->names as $name => $index) {
              if ($subject == $index) {
                  return $name;
              }
          }
  
          return $subject + 1;
      }
docs: Turns an internal array index into the frames list,
  into a public name, or if none, then a one offset index.
  
  @param int $subject    Internal index.
  
  @return integer/string     Public name.