common\ModuleExtraType::getPossibleTypes PHP Method

    public static function getPossibleTypes()
    {
        $possibleTypes = [self::BLOCK, self::HOMEPAGE, self::WIDGET];
        return $possibleTypes;
    }

 /**
  * @param string $type
  * @return self
  */
 public static function withType($type)
 {
     return new self(sprintf('%s is not a valid module extra type. Possible options are %s', $type, implode(', ', ModuleExtraType::getPossibleTypes())));
 }