What is #bags,#messages?

当我进行服务器端验证时，我正在转储$errors数组。你能解释一下这种数组格式吗？#标签是什么意思？

ViewErrorBag {#135 ▼
  #bags: array:1 [▼
    "default" => MessageBag {#136 ▼
      #messages: array:5 [▼
        "fullname" => array:1 [▼
          0 => "The fullname field is required."
        ]
        "email" => array:1 [▼
          0 => "The email field is required."
        ]
        "username" => array:1 [▼
          0 => "The username field is required."
        ]
        "password" => array:1 [▼
          0 => "The password field is required."
        ]
        "gender" => array:1 [▼
          0 => "The gender field is required."
        ]
      ]
      #format: ":message"
    }
  ]
}