Yeah, I didn't know it originally, it's using the LaTeX pretty printer and it is working correctly, so the generic pretty printer template is perfect for \vec :)

I'm cool with parenthesis;

Not definitive but it looks like ASCII Math just uses "vec x" with a space to denote this type of vector.

http://www1.chapman.edu/~jipsen/mathml/asciimathsyntax.html

['vec ',''] ?