subText property Null safety
Provides some additional information that is displayed in the notification.
No guarantees are given where exactly it is displayed. This information should only be provided if it provides an essential benefit to the understanding of the notification. The more text you provide the less readable it becomes. For example, an email client should only provide the account name here if more than one email account has been added.
As of Android 7.0 this information is displayed in the notification header area. On Android versions before 7.0 this will be shown in the third line of text in the platform notification template. You should not be using setProgress(int, int, boolean) at the same time on those versions; they occupy the same place.
final String? subText;