[NTG-context] Is this font changing allowed/correct?

Can I switch fonts like this? I know something is wrong because it doesn't work ('concrete' typeface is not used), but I would like to know if I'm in the right direction. Thanks, Maurício %%% \usetypescriptfile[type-gentium] \usetypescriptfile[type-otf] \usetypescript[gentium] \usetypescript[concrete] \setupbodyfont[gentium,20pt] \starttext Some text. { \switchtobodyfont[concrete] More text. } \stoptext %%%