I've seen this style of commit on and off for a while now. I'm not a huge fan, but I get the idea. What I hadn't realised is that there was a "standard" behind this and even some documentation for it.
A proposed standard for "docstrings" for TypeScript. Well, not docstrings in the Lisp/Python sense, but comments that can be used to document an API in place and allow for the generation of documentation from them.