I've used LaTeX quite a long time but recently I begin to use ConTeXt too.
So I'm very sorry if the following is well-known issue.

I find an example of \pmatrix in p.21 of "ConTeXt Mark IV an excursion"
(ma-cb-en.pdf).  And I notice it is defined in
/usr/share/texmf/tex/context/base/mkiv/math-pln.mkiv (in Debian).
But it seems \bmatrix, \vmatrix are not defined yet.
Is there any reason why they are not defined?
Similar commands or environments \begin{bmatrix}...\end{bmatrix},
\begin{vmatrix}...\end{vmatrix} are very often used in mathematical
LaTeX documents.
It is very useful if we can use \bmatrix and \vmatrix in ConTeXt
documents, so please add
\unexpanded\def\bmatrix#1%
  {\left[\matrix{#1}\right]}
\unexpanded\def\vmatrix#1%
  {\left|\matrix{#1}\right|}
in math-pln.mkiv or somewhere.

By the way, I think it is critical to set
\setupmathematics[ampersand=normal]
to use \matrix above but I can't find this setting in ma-cb-en.pdf
It is great if this is added in  ma-cb-en.pdf