Thanks Wolfgang. I could even have sections in the TOC  with
'\setuptexttexts[{\placerawheaddata[section]}]'.

However, how can I start a new page at each new section? The 'page=yes'
pair does no longer work with your solution 'placehead=hidden' (since the
head is not placed I guess). I also tried 'before=\page' or 'after=\page'
without more success. Here is a minimal example showing the absence of page
breaks though I specified 'page=yes' (the section numbers are also
mismatched but if one puts manual page breaks they match again, so it's not
really a problem for me):


\setupheadertexts[\namedstructurevariable{section}{title}][]

\setuphead
  [section]
  [placehead=hidden,
   page=yes] % <-- This key does NOT work.

\setuphead
  [subsection]
  [placehead=yes,
   before={\blank[line]},
   after={\blank[line]}]

\setuptexttexts[{\placerawheaddata[section]}]

\showframe

\starttext
\completecontent
\dorecurse{2}
  {\section{My section}
   \dorecurse{2}
     {\subsection{My subsection}
      \input knuth}}
\stoptext