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

[Thomas A. Schmitz]

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