From Xojo Documentation
|This event is only available for Web applications.|
The CheckBox has been clicked or the value has been changed programmatically. A right-click does not trigger the Action event.
This is the equivalent of the desktop Checkbox.Action event.
If the the CheckBox value has been changed, either programmatically or by the user, then you may want to also cause another action to occur. In this event, you can take the action you need. This code in the ValueChanged event could be used to update a Session preference value based on the CheckBox setting:
This code in the ValueChanged event makes a TextArea read-only based on a CheckBox setting: