original_string: protected function checkValidHeader($key, $value, &$error) {
      if (!is_string($key)) {
        $error = sprintf("Header key is not a string (Actual type: %s).",
                         gettype($key));
        return false;
      } else if (!in_array(strtolower($key), self::$allowed_headers)) {
        // Array keys don't have consistent case.
        $error = sprintf("Input header '%s: %s' is not whitelisted for use with" .
                         " the Google App Engine Mail Service.",
                         htmlspecialchars($key),
                         htmlspecialchars($value));
        return false;
      }
      return true;
    }
code: protected function checkValidHeader($key, $value, &$error) {
      if (!is_string($key)) {
        $error = sprintf("Header key is not a string (Actual type: %s).",
                         gettype($key));
        return false;
      } else if (!in_array(strtolower($key), self::$allowed_headers)) {
        // Array keys don't have consistent case.
        $error = sprintf("Input header '%s: %s' is not whitelisted for use with" .
                         " the Google App Engine Mail Service.",
                         htmlspecialchars($key),
                         htmlspecialchars($value));
        return false;
      }
      return true;
    }
code_tokens: protected function checkValidHeader ( $ key , $ value , & $ error ) { if ( ! is_string ( $ key ) ) { $ error = sprintf ( "Header key is not a string (Actual type: %s)." , gettype ( $ key ) ) ; return false ; } else if ( ! in_array ( strtolower ( $ key ) , self :: $ allowed_headers ) ) { // Array keys don't have consistent case. $ error = sprintf ( "Input header '%s: %s' is not whitelisted for use with" . " the Google App Engine Mail Service." , htmlspecialchars ( $ key ) , htmlspecialchars ( $ value ) ) ; return false ; } return true ; }
docstring: Check validity of a header pair.
  
  @param string $key Header key.
  @param string $value Header value.
  @param string &$error Error message to be set if the header is invalid.
  @return bool True if successful, false otherwise.
docstring_tokens: Check validity of a header pair .