Chapter head with absolute positioning of following text

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\setuphead[chapter][before=\vbox to 4cm\bgroup,after=\vss\egroup]
\starttext
\chapter{test} \input tufte
\stoptext

No matter how many lines the chapter head runs to, the text will always start, e.g. 4cm below the top of the heading:

[edit] Bug and proposed workaround

I tried this sample and \getmarking[chapter], used in my headers, stopped to work properly. Proposed workaround below. --SeR 00:52, 27 January 2006 (CET)

\def\MyChapterCommand#1#2{\vbox to 4cm\bgroup
                                                                         {#1\hskip.75em #2}
                                                                         \vss
                                                                      \egroup}
\setuphead[chapter][header=nomarking,command=\MyChapterCommand]
\starttext
\chapter{test} \input tufte
\stoptext