Anchoring layer

["Thomas A. Schmitz" <thomas.schmitz@uni-bonn.de>]

I'm trying to write a module that will mimick the behavior of  
crop.sty in LaTeX (providing fancier cropmarks than the ones given by  
the ConTeXt \setuplayout command). I'm done with the code for the  
cropmarks, and this is working fine. Now I want to have a status line  
in between the two top marks. How can I give an absolute position for  
a layer that will put this line midaligned and exactly, say 0.5cm  
above the level of the upper corners of the page? What I tried so far  
is:
\composedlayer and something like \setlayer[y=2cm] - will only be on  
the first page, not repeated;
\framed - I can give the frame a height like 1.3\textheight, but then  
the position will not be fixed, but change with the textheight

I guess there must be a trivial solution, but I haven't found it yet...

Best

Thomas