On Sun, 14 Feb 2021, Jigé wrote:

> Hi all.
> 
> I'm trying to place a TikZ picture in the margin.
> Here is a small example:
> 
> \usemodule[tikz]
> \setuplayout[backspace=4cm, topspace=2cm, height=middle]
> \starttext
> \input{lorem}
> \margintext{I have discovered a truly
>             marvelous proof ...  but
>             this margin is too narrow
>             to contain it.}
> \input{lorem}
> \inmargin{\externalfigure[cow] [width=\marginwidth]}
> % The above works.
> % The following does not:
> \input{lorem}
> \inmargin{
> \starttikzpicture
>   \draw[gray] (-2,0) grid (2,2) ;
>   \draw plot [domain=-2:2, samples=50, smooth] (\x,{\x * \x});
> \stoptikzpicture
> }
> \stoptext
> 
> -> Undefined control sequence

Most likely because the argument of \inmargin is scanned upfront and at that time \draw etc are undefined. One option is:

\startbuffer[picture]
\starttikzpicture
...
\stoptikzpicture
\stopbuffer

\inmargin{\getbuffer[picture]}

Another option (but better to do that in tikz module) is:

\let\draw\relax
\let\x\relax

\inmargin{\starttikzpicture ... \stoptikzpicture}

> Actually the command \startmarginblock ... \stop... described in the ConText reference works with a TikZ picture. 

Because the \start ... \stop blocks don't scan the argument.

Aditya