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The BeforeUpdate event fires when the user has pressed Enter during an edit to apply his or her changes but before the changes are actually applied. This gives you the opportunity to perform validation on the changes. If you decide the changes should not be applied, then set the Cancel property to 1 or 2 to prevent the update and keep the user in edit mode. It's very important that you qualify this event as synchronous. Otherwise, it's impossible to cancel the edit.
