Hi Hans,
If I do this, the problem remains the same.

\starttikzpicture
  \vbox{\matrix [matrix of math nodes,ampersand replacement=\&]
  {
    a_8 \& a_1 \& a_6         \\
    a_3 \& a_5 \& |[red]| a_7 \\
    a_4 \& a_9 \&     a_2     \\
  };}
\stoptikzpicture

2016-07-21 11:38 GMT+02:00 Hans Hagen <pragma@wxs.nl>:

> On 7/21/2016 11:25 AM, Fabrice Couvreur wrote:
>
>> Hello,
>> Everything is in the title, as this example shows.
>>
>
> normally it means that you need to wrap in a \vbox{...}
>
> Thanks,
>> Fabrice
>>
>>
>> ####################################################################
>> \usemodule[tikz]
>> \usetikzlibrary[matrix]
>>
>> \setupbodyfont[pagella,11pt]
>>
>> \starttext
>>
>> \starttikzpicture
>>   \matrix [matrix of math nodes,ampersand replacement=\&]
>>   {
>>     a_8 \& a_1 \& a_6         \\
>>     a_3 \& a_5 \& |[red]| a_7 \\
>>     a_4 \& a_9 \&     a_2     \\
>>   };
>> \stoptikzpicture
>>
>> \stoptext
>>
>> ####################################################################
>> tex error       > tex error on line 14 in file /home/fab/ntg49.tex: !
>> Argument of \tikz@lib@matrix@with@options has an extra }
>>
>> <inserted text>
>> \par
>> <to be read again>
>> }
>> l.14   }
>>       ;
>>
>>  4     \setupbodyfont[pagella,11pt]
>>  5
>>  6     \starttext
>>  7
>>  8     \starttikzpicture
>>  9       \matrix [matrix of math nodes,ampersand replacement=\&]
>> 10       {
>> 11         a_8 \& a_1 \& a_6         \\
>> 12         a_3 \& a_5 \& |[red]| a_7 \\
>> 13         a_4 \& a_9 \&     a_2     \\
>> 14 >>    };
>> 15     \stoptikzpicture
>> 16
>> 17     \stoptext
>>
>>
>>
>>
>>
>> ___________________________________________________________________________________
>> If your question is of interest to others as well, please add an entry to
>> the Wiki!
>>
>> maillist : ntg-context@ntg.nl /
>> http://www.ntg.nl/mailman/listinfo/ntg-context
>> webpage  : http://www.pragma-ade.nl / http://tex.aanhet.net
>> archive  : http://foundry.supelec.fr/projects/contextrev/
>> wiki     : http://contextgarden.net
>>
>> ___________________________________________________________________________________
>>
>>
>
> --
>
> -----------------------------------------------------------------
>                                           Hans Hagen | PRAGMA ADE
>               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
>        tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
> -----------------------------------------------------------------
>
> ___________________________________________________________________________________
> If your question is of interest to others as well, please add an entry to
> the Wiki!
>
> maillist : ntg-context@ntg.nl /
> http://www.ntg.nl/mailman/listinfo/ntg-context
> webpage  : http://www.pragma-ade.nl / http://tex.aanhet.net
> archive  : http://foundry.supelec.fr/projects/contextrev/
> wiki     : http://contextgarden.net
>
> ___________________________________________________________________________________