code: public function getErrorSummary($showAllErrors)
      {
          $lines = [];
          $errors = $showAllErrors ? $this->getErrors() : $this->getFirstErrors();
          foreach ($errors as $es) {
              $lines = array_merge((array)$es, $lines);
          }
          return $lines;
      }
docs: Returns the errors for all attributes as a one-dimensional array.
  @param bool $showAllErrors boolean, if set to true every error message for each attribute will be shown otherwise
  only the first error message for each attribute will be shown.
  @return array errors for all attributes as a one-dimensional array. Empty array is returned if no error.
  @see getErrors()
  @see getFirstErrors()
  @since 2.0.14