Is this a custom object type? if so, how do you create them?
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while printing an object from some API output, I saw that instead of array or stdClass, it was a custom object type.

    [_unsavedValues:protected] => Stripe_Util_Set Object
        (
            [_elts:Stripe_Util_Set:private] => Array()
        )

can someone explain how this is different from a regular object and how it is created?