Generate Authorlist from Head Content

With the new head syntax (MkIV) one can easy add information to chapters, sections, etc.

Here is an example from Wolfgang Schuster ([1])

\define[3]\ChapterList
 {\bTABLE[offset=0pt,strut=yes,frame=off,width=.5\textwidth]
    \bTR
      \bTD \structurelistuservariable{date} \eTD
      \bTD #2 \eTD
      \bTD (\structurelistuservariable{author}) \eTD
    \eTR
  \eTABLE}

\setuplist
  [chapter]
  [alternative=command,
   command=\ChapterList]

\define[2]\ChapterHead
  {\startframedtext[frame=off,width=broad,offset=0pt,align=middle]
     \doifsomething
       {\structureuservariable{date}}
       {\structureuservariable{date}\blank}
       #2
     \doifsomething
       {\structureuservariable{author}}
       {\blank\structureuservariable{author}}
   \stopframedtext}

\setuphead
  [chapter]
  [command=\ChapterHead]


\starttext

\completecontent

\startchapter[title=Rom][date=12.06.2010,author=Knuth]
  \input knuth
\stopchapter

\startchapter[title=Pisa][date=14.06.2010,author=Tufte]
  \input tufte
\stopchapter

\stoptext