What does this array expression mean?

Question

 protected $databaseRule = [

        'hostname' => 'require',

        'database' => 'require',

        'hostport' => 'require|number',

        'username' => 'require',

        'prefix'   => 'require|regex:/^[a-z0-9] [_]{1}/',

    ];

    protected $databaseMssage = [

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Answer 1

The array key name is just an ordinary string. As for characters with special meanings added in the middle, such as dots, its meaning is defined by its user. It can be understood as the prefix