InfoPath's validation events are, not surprisingly, intended to be used in the validation of InfoPath form data. There are three validation events: OnBeforeChange, OnValidate, and OnAfterChange, which occur in that order.
▸ Validation of InfoPath form data is described in Chapter 10, “Validating Form Data,” p. 179.
The DataDOMEvent object is passed as an argument to each of the three InfoPath validation events.
The OnBeforeChange Event
The OnBeforeChange event is the first of the three validation events to occur when the user makes a change in the values visible in a form control. The OnBeforeChange ...