\setupbodyfont[lmodern]
\starttext
\type{$\lbrace$} <$\lbrace$>\crlf
\type{$\lbrack$} <$\lbrack$>\crlf
\stoptext
This does typeset a left brace but chokes on \lbrack.
I took my copy of the TeX Book and find \brack as one of the defined delimiters in chapter 17. How come?
ConTeXt ver: 2010.03.20 22:59 MKIV fmt: 2010.3.21 int: english/english
fonts : preloading latin modern fonts
bodyfont : 12pt rm is loaded
language : language en is active
systems : begin file test.tex at line 2
! Undefined control sequence.
<recently read> \lbrack
l.4 \type{$\lbrack$} <$\lbrack
$>\crlf
?