To receive a notification, a user or group must subscribe to that notification type from a particular source. For example, you may want to create a subscription that notifies all Administrators via private message when something has been added to the Continua Event Log:
Creating and Editing Subscriptions
Group
Members of the group will receive the notification, provided that they have an specified an email or XMPP address specified, and so long as they don't have a user-level subscription for the same notification type.
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The entity that the notification is about. The notifications types available depend on on the type of the source that you select.
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