count option-fields vs check-boxes

I refer to the count-checkboxes code mentioned here.

I use Option-Fields instead to make only one activated checkbox valid.

How do I change the code to "read" all option-fields?

var nSum = 0;var aCkFlds = this.getField("checkn").getArray();for(var i=0;i<aCkFlds.length;i++){if(aCkFlds[i].isBoxChecked(0))nSum++;}event.value = nSum;