evaluate button array by each member

[bbxrider]

before calling a validation function i assign a custom property to the form
elements
to determine if its a required field
this.form.xxx.req=true
if its a button i assign to all the buttons for that name
this.form.xbutton[0].req=true
this.form.xbutton[1].req=true...........

the validate function is called with 'this.form',
validate(this.form)
validate(f)...................................
then i use f.name, f.value, etc

but i can't figure out how to access the radio buttons as array members in
the validate function
f.xbutton[x] - doesn't work
self.document.forms[x].elements[x].name[x] - doesn't work either

seems simple but i'm obviously missing something