[NTG-context] How to implement a changing navigation bar?

Hi all, I use an overlay to implement a navigation bar in the left margin of a document. It seems to me that the processing of the overlay is done only once and not for every page again. In addition, the \lastpage is not available. Does anyone know a solution? Maybe headers/footers are a solution. But how is absolute positioning accomplished with them? Thanks for your attention, --Stefan PS: Here is my current implementation: \definelayer[navbar] \setupbackgrounds[text][leftmargin][background=navbar] \setlayer[navbar][x=0cm,y=10cm]{\the\pageno}