Overtrue\Validation\MessageBag::add PHP Method

    public function add($key, $message)
    {
        if ($this->isUnique($key, $message)) {
            $this->messages[$key][] = $message;
        }
        return $this;
    }

 /**
  * Add an error message to the validator's collection of messages.
  *
  * @param string $attribute
  * @param string $rule
  * @param array  $parameters
  */
 protected function addError($attribute, $rule, $parameters)
 {
     $message = $this->getMessage($attribute, $rule);
     $message = $this->doReplacements($message, $attribute, $rule, $parameters);
     $this->messages->add($attribute, $message);
 }