[NTG-context] how can I use framewidth in calculations

Hi all, maybe I'm overlooking something obvious, but...: when I have a figure, I can calculate its width dependent on the page width, and it will adapt: \starttext \externalfigure[cow][width=0.6\textwidth] \stoptext But is there a method for similar calculations inside a frame? Here's what I tried, but it doesn't give the expected result (the image is much smaller than expected): \starttext \framed[width=7cm]{\externalfigure[cow][width=\the\dimexpr0.9\framedparameter{width}\relax]} \stoptext Thanks for any pointers! Thomas