[NTG-context] Getting dimensions in Lua

Hi, list. I want to get some dimensions in Lua. See, for instance \starttext \the\dimexpr\availablehsize\relax %say, 426pt \stoptext Is there an equivalent in ConTeXt for Lua, i.e. without passing values from TeX or, at least, using only Lua commands? Thank you in advance. Best wishes, Jairo