Sokil\Mongo\Structure::addError PHP Method

    public function addError($fieldName, $ruleName, $message)
    {
        $this->errors[$fieldName][$ruleName] = $message;
        return $this;
    }

 public function validateField(Structure $document, $fieldName, array $params)
 {
     $value = $document->get($fieldName);
     if (!$value) {
         return;
     }
     if (!isset($params['min'])) {
         throw new Exception('Minimum value of range not specified');
     }
     if (!isset($params['max'])) {
         throw new Exception('Maximum value of range not specified');
     }
     if ($value < $params['min']) {
         if (empty($params['minMessage'])) {
             $params['minMessage'] = 'Field "' . $fieldName . '" less than minimal value of range in ' . get_called_class();
         }
         $document->addError($fieldName, $this->getName(), $params['minMessage']);
     }
     if ($value > $params['max']) {
         if (empty($params['maxMessage'])) {
             $params['maxMessage'] = 'Field "' . $fieldName . '" less than minimal value of range in ' . get_called_class();
         }
         $document->addError($fieldName, $this->getName(), $params['maxMessage']);
     }
 }