That looks great, it's a pet peeve of mine that it's difficult to format languages that are encased in another language. Most (all?) editors are only expecting a single "language" in a file. You have a js file? Must contain only JavaScript!
Unrelated to 1.13 but thanks to the release notes, I now know about Zigler; which looks really neat.
https://github.com/ityonemo/zigler
