[NTG-context] markings and syncing

[Thomas A. Schmitz]

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