[NTG-context] self defined conversion in \date

Hi, It seems, that you cannot use self defined conversions in \date: \defineconversion[mytest][X-\romannumerals] \starttext Self defined conversion: \convertnumber{mytest}{1} (OK)\\ Predefined conversion in date: \date[d=1][day:a] (OK)\\ Self defined conversion in date: \date[d=1][day:mytest] (not OK) \stoptext Is this a bug, or a feature? How could one use self defined conversions in \date please? TIA for any help, -- Peter