[NTG-context] vertical alignment in the header text

Dear all, In the following sample, header text located at the top of the header. But, I'd like to align the header text in vertical center. I tried \dontleavehmode, \vfill, top=\vss, etc, but I couldn't succeed. %%%%%%%% \setuplayout[header=1cm, width=18cm, backspace=1.5cm] \setupbackgrounds[header][text][bottomframe=on,topframe=on] \setupheadertexts[][header\hfill header\hfill header] \setuppagenumbering[location=footer] \starttext \input knuth \stoptext %%%%%%%% How to control the vertical alignment in the header? Thank you. Best regards, Dalyoung