\starttext

\section{test}

\unexpanded\def\whatever#1#2{[#1][#2]}

\setuphead[section][command=\whatever]

\section{test}

\defineheadplacement[whatever]#1#2{(#1)(#2)}

\setuphead[section][command=,alternative=whatever]

\section{test}

\defineheadalternative
  [whatever]
  [alternative=vertical,
   renderingsetup=whatever]

\startsetups[whatever]
    /\headnumbercontent/\headtextcontent/
\stopsetups

\setuphead[section][command=,alternative=whatever]

\section{test}

\stoptext
