Multi select check box in repeater

It has to be obvious but I can't find it. In CF6 one could add a check box field name using

fieldname[]

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to allow selection of multiple values. You can't add that in CF7. It rejects the square brackets.
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So - how does one use multiselect in CF7 check boxes in a repeater??
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Nick

I have found a work round for this - add an html attribute 'name'

fieldname[]

leaving the check box field name blank.
I doubt that this is the 'correct' solution but it seems to work.
Nick