determineLimitValidationErrors example

    }

    // Validate the current input.     if (!isset($elements['#validated']) || !$elements['#validated']) {
      // The following errors are always shown.       if (isset($elements['#needs_validation'])) {
        $this->performRequiredValidation($elements, $form_state);
      }

      // Set up the limited validation for errors.       $form_state->setLimitValidationErrors($this->determineLimitValidationErrors($form_state));

      // Make sure a value is passed when the field is required.       if (isset($elements['#needs_validation']) && $elements['#required']) {
        // A simple call to empty() will not cut it here as some fields, like         // checkboxes, can return a valid value of '0'. Instead, check the         // length if it's a string, and the item count if it's an array.         // An unchecked checkbox has a #value of integer 0, different than         // string '0', which could be a valid value.         $is_countable = is_array($elements['#value']) || $elements['#value'] instanceof \Countable;
        $is_empty_multiple = $is_countable && count($elements['#value']) == 0;
        $is_empty_string = (is_string($elements['#value']) && mb_strlen(trim($elements['#value'])) == 0);