If the UpdateMode property is set to "Always", the UpdatePanel control’s content is updated on each postback that starts from anywhere on the webpage. This also includes asynchronous postbacks from controls that are inside other UpdatePanel controls, and postbacks from controls which are not inside UpdatePanel controls.
If the UpdateMode property is set to Conditional, the UpdatePanel control’s content is updated when one of the following is true:
1 - When the postback is caused by a trigger for that UpdatePanel control.
2 - When you explicitly call the UpdatePanel control's Update() method.
3 - When the UpdatePanel control is nested inside another UpdatePanel control and the parent panel is updated.
When the ChildrenAsTriggers property is set to true and any child control of the UpdatePanel control causes a postback. Child controls of nested UpdatePanel controls do not cause an update to the outer UpdatePanel control unless they are explicitly defined as triggers for the parent panel.
Controls defined inside a
If the ChildrenAsTriggers property is set to false and the UpdateMode property is set to Always, an exception is thrown. The ChildrenAsTriggers property is intended to be used only when the UpdateMode property is set to Conditional.