1. The bordermatrix code is part of the core and you can remove it from 
cont-new.mkiv.

2. To use the \equalign command you have to enable the special meaning 
of & in math mode with \setupmathematics[ampersand=normal].

3. User the new mathalignment environment as replacement for \equalign 
which avoids special characters like &.

Wolfgang
> Fabrice L <mailto:fabrice.alpha@gmail.com>
> 19. April 2018 um 22:05
> Dear list,
>
> Some months ago, Hans wrote to this list (see below) a macro to do 
> matrix showing outside the brackets some informations (like we usually 
> do for Markov chains), but adapted some plain tex code, which worked 
> in MKII). I have used with success this code since then, but some 
> weeks ago, the behavior of Context had changed (probably something on 
> my part; I have updated the installation, but nothing changed).
>
> The problem (I think) is linked to \unprotect \protect. When this code 
> is put before the \starttext to the the cont-new-mkiv, the border 
> matrix behave well, but a simple \eqalign like this:
>
> \startformula
> \eqalign{ & \lambda=5, \mu =5 \cr
> & \mu=8 \cr }
> \stopformula
>
> do not works is I replace «  \lambda » by « \lambda_2 » for example. I 
> have no idea what’s is going on. here is a minimal example where 
> Hans’s code is before the \starttext:
>