Dear list

I'm sorry if that's the wrong list, but mlpost doesn't seem to have
it's own list.

I'm starting to use (quite happily!) MLPost for some drawing, and it
works perfectly. But now I'm trying some more advance things, and I'm
stuck:

I would like to draw variable size curly braces, pretty much like
\underbrace would do in LaTeX. More specifically, I want to draw 16
boxes horizontally alligned (representing 16 bits of a VM
instruction), and "select" (by a curly brace) say the 4 first and say
it's the opcode, and then the 12 next and say it's the argument.

How could I do that?

Thanks in advance.

Alexandre Pilkiewicz