code: public function getValidationAttributes($attributes = null)
      {
          if ($attributes === null) {
              return $this->getAttributeNames();
          }
  
          if (is_string($attributes)) {
              $attributes = [$attributes];
          }
  
          $newAttributes = [];
          $attributeNames = $this->getAttributeNames();
          foreach ($attributes as $attribute) {
              if (in_array($attribute, $attributeNames, true)) {
                  $newAttributes[] = $attribute;
              }
          }
          return $newAttributes;
      }
docs: Returns a list of attributes this validator applies to.
  @param array|string|null $attributes the list of attributes to be validated.
  
  - If this is `null`, the result will be equal to [[getAttributeNames()]].
  - If this is a string or an array, the intersection of [[getAttributeNames()]]
  and the specified attributes will be returned.
  
  @return array list of attribute names.
  @since 2.0.16