[NTG-context] markings and syncing

Hi, I'm trying to set up a header: if a page contains only one marking, it should display this, if it has more than one, display the first and last. Here's what I tried, unsuccessfully: \definemarking [test] \startsetups [test header] \doifelse {\expanded{\getmarking[test][top]}} {\expanded{\getmarking[test][bottom]}} {\getmarking[test][top]} {\getmarking[test][top] and \getmarking[test][bottom]} \stopsetups \setupheadertexts [\setups{test header}] \starttext \marking[test] {One} \input knuth \marking [test] {Two} \page \marking [test] {Three} \input tufte \stoptext How can I make the \doifelse work? I'm not sure I understand the keywords top/bottom, first/last, and previous/next. Thomas