It's the `'text'` pretty printer template. The LaTeX pretty printer is here: https://github.com/devlin/mathquill/blob/4bfee7fd95b18cdf48c3d13c9701e4c63063bcdd/src/math.js#L287

Basically, it starts with `this.ctrlSeq`, then adds `{}` around the child block's LaTeX, which I believe will do exactly the right thing in this case.