Also when you tap these notifications they will activate said application, so if they're from installing an app from Google Play you can tap them to start the application. If they're Google Play app updates tap to open Google Play to update said applications, if they're a movie, book or magazine they will open that application so the content can be viewed. Obviously email and Gmail notifications open that application to view your emails and any of these notifications can be removed from the notification pulldown singularly too by swiping that particular notification to the left or right.
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