[NTG-context] centered headertexts ??

Hi, apologies, I guess this one is a pretty easy question, but after trying (almost) every combination I gave up... How do I get xxx and yyy set in the header's center?? \setuppagenumbering [alternative=doublesided,location= {header,marginedge}] \setupheadertexts[][xxx][yyy][] \starttext \input tufte \input knuth \input tufte \input knuth \input tufte \input knuth \stoptext As always, thank you very much, Steffen