Dear Weber Mattias,

Please see page 10 of “mathalign.pdf” made by Aditya.
He showed the way of writing  aligned math including  matrices.
For example,

\startformula

 \startmatrix[left={\left(\,},right={\,\right)}]

      \NC 1 \NC 0 \NC 0 \NR
      \NC 0 \NC 1 \NC 0 \NR
      \NC 0 \NC 0 \NC 1 \NR
    \stopmatrix 
  \stopformula 
There are many other examples that you can use.

Best regards,
Dalyoung

> Message: 2
> Date: Sun, 3 May 2020 17:47:24 +0000
> From: "Weber, Matthias" <matweber@indiana.edu>
> To: mailing list for ConTeXt users <ntg-context@ntg.nl>
> Subject: [NTG-context] Vertical lines in matrices
> Message-ID: <C8902576-CF86-4967-8A1B-DFF66615DA37@indiana.edu>
> Content-Type: text/plain; charset="utf-8"
> 
> Dear List,
> 
> I am trying to get vertical (separating) lines into matrices, as is possible in tables:
> 
> \starttext
> \startformula
> \left(
> \starttable[|c|c|c|]
> \NC 0 \NC  0\VL  0 \FR
> \NC 1 \NC  0\VL  1 \FR
> \stoptable
> \right)
> \stopformula
> \stoptext
>