\starttext

    \setuplistalternative[c][filler=sym]    \placelist[chapter][alternative=c]
    \setuplistalternative[c][filler=symbol] \placelist[chapter][alternative=c]
    \setuplistalternative[c][filler=width]  \placelist[chapter][alternative=c]
    \setuplistalternative[c][filler=space]  \placelist[chapter][alternative=c]
    \setuplistalternative[c][filler=rule]   \placelist[chapter][alternative=c]

    \definefiller
      [whatever]
      [symbol]
      [filler=symbol,
       symbol=\hbox to .25em{\periodcentered},
       color=darkred,
       style=\bf]

    \setuplistalternative[c][filler=whatever]
    \placelist[chapter][alternative=c]

    \chapter{test a}
    \chapter{test b}
    \chapter{test c}

\stoptext
