there is only one element in the form, but it must be accessed thru array

Hi guys, as you can see from the attached image, I have one checkbox(ToCheckInOut) in the form CheckInOutForm. Before IE10, I could access the checked attribute of this checkbox by CheckInOutForm.ToCheckInOut.checked, but in IE10 Compat View and IE5 quirks, it doesn't work any more. Why it becomes an array when there is only one checkbox in this form?