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Hyperlink tag is always the item to find look up to process check how the event on is processed (Notify or go to depending on THAT item's flags). This could be the item itself or someone else. NOTIFY or GOTO).
If item wants to be notified (MESSAGEBAR_NOTIFY) then Hyperlink tag is the string to call NavNotifyItem on e.g. "MESSAGEBAR\NotificationWarning". So basically the target and notify items are the same.
If item doesn't want notification then target item's description is used in a call to NavGotoItem.
If the item is inserted with USERXAML, then the tag is specified by the user in the XAML. If it's not custom XAML,then the Hyperlink tag is made from the FQN of the item (
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Made of the parent and 2nd argument to NavInsertItem)
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For the target item
If MESSAGEBAR_NOTIFY flag, then Hyperlink tag is the object to notify e.g. "MESSAGEBAR\NotificationWarning". So basically the target and notify items are the same. This is an item that's been inserted with NavINsertItem.
If not MESSAGEBAR NOTIFY then target item's description is the nav location to go to