>It will fire the QueryUnload of the Form and, if memory serves me right, if you
>return .F. the close operation is aborted.

That's a common misconception which I used to share.

Form.QueryUnload

LOCAL llRetVal

llRetVal = .T.
IF ThisForm.JobCompleted = .F.
    NODEFAULT
    llRetVal = .F.
ENDif

RETURN llRetVal

Form.cmdClose.Click

IF ThisForm.QueryUnload()
    ThisForm.Release()
ENDif

The NODEFAULT is what stops the unload: returning .F. is only useful if you add code to your exit button.