code: public static function email($email = null, $errorMsg = null)
      {
          if (!$email) return null;
  
          // Convert to lowercase and set UTF-8 character encoding
          $email = trim(mb_strtolower(trim($email), "UTF-8"));
  
          // Validate email address
          if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
              return null;
          }
          // Return email address
          return $email;
      }
docs: Validates and returns sanitized email address.
  
  @param null|string $email User's input email address.
  @param null|string $errorMsg Optional user's error message for invalid email address.
  @return string