ChildExpanded Event
The ChildExpanded event is the same as the Expanded event, but it is sent to the parent of the TreeviewField.
This event has the following syntax:
on childexpanded [compositefieldname]
compositefieldname is optional if you specify the event in a script for a composite field, or if the composite field is the frame's top form.
The TriggerNode attribute identifies the node that was expanded.
Usage: The ChildExpanded event occurs when a node has been expanded to show it's child nodes by clicking the small “expand” box [+] adjacent to the node. The ChildExpanded event can be used to populate or modify the child nodes for the expanded node.
More information: