This is a docstring annotation on a value (rather than a definition)? And what we recognize as comment syntax from C could also equivalently be, say, an `anno` keyword or punctuation, followed by a more familiar string literal?

  let x = 40 + 2 /* the number fourtytwo */;

  let x = 40 + 2 anno "the number fourtytwo";

  let x = 40 + 2 @"the number fourtytwo";