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# identifier

The unique string assigned to the category.

```
var identifier: String { get }
```

## Discussion

Use this string to differentiate the different types of notifications that your app can send. To assign a category to a local notification, assign this string to the [`categoryIdentifier`](/documentation/UserNotifications/UNMutableNotificationContent/categoryIdentifier) property of the content object. To assign a category to a remote notification, use the string as the value of the `category` key in the notification payload `aps` dictionary.

---

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