<texcode>
\definereferenceformat[cite][left={[},right={]}]
\defineitemgroup [bibliography] [levels=1]\setupitemgroup [bibliography][each]
[symbol=n,
left={[},
\appendtoks
\let \bibitem \itemgroupitem \let\startbibitem \startitemgroupitem \let\stopbibitem \stopitemgroupitem
\to \itemgroupcommands
</texcode>