Am 06.09.2010 um 19:57 schrieb Cecil Westerhof:

I start to understand it. Thanks.

I changed it a little. I implemented 'title'. And with startitemize I
got empty space between my 'title' and the checkboxes.

The blank line comes from itemize, you can get rid of it with \startitemize[joinedup].

So I coded it
like:
   \def\CheckBoxes[#1,#2]%
    {#1\par
     \processcommalist[#2]\doCheckBoxes
    }

[...]

Is there a way that I do not need al the '\blank' lines. After a
checkbox list, I always want an empty line.

Add \blank at the begin and end of your macro:

\def\CheckBoxes[#1][#2]%
  {\blank
   #1\par
   \processcommalist[#2]\...
   \blank}

I wonder why need this command when can get the same result with normal context commands:

\definesymbol[checkbox][{[~~~]}]
\defineitemgroup[checkbox]
\setupitemgroup[checkbox][each][packed][margin=2.5em,symbol=checkbox,width=1.5em,distance=.5em]

\starttext

\startcheckbox
\nop title
\item Yes
\item No
\item A little bit
\stopcheckbox

\stoptext

Wolfgang