[NTG-context] Getting font parameters in MkIV

Dear all, how can I access font parameters (e.g. the thickness of the fraction rule) of an OpenType font in MkIV? Taco once gave me the solution: --- \usetypescript[cambria] \setupbodyfont[cambria] \def\defaultrulethickness{\the\fontdimen8\textfont3\relax} \starttext \the\defaultrulethickness \stoptext --- which used to work in the old MkII days. Now with MkIV I get: --- ! Font \nullfont has only 7 fontdimen parameters. <to be read again> \relax l.10 \the\defaultrulethickness ? --- What's the new method to obtain the desired parameters? Best wishes, Oliver