[NTG-context] setupcite in mkiv to cite two references

Hi list, I need some help about formatting citations in mkiv. What I want is something like [3, 4] if I put \cite[ref3,ref4]. However, what I actually get is [3 and 4]. This only happens if I put two references in \cite[]. So, does anyone know how to replace 'and' with ', ' in my situation. best, Yu