[omaranto]

This explanation of how %r works here is incorrect:

> I knew about `%r` but hadn't realized that it escapes forward-slashes while leaving other regex symbols intact.

The correct explanation can also be found in the next sentence of your comment:

> But with the previous explanation of `%q`, in which arbitrary delimiters can be used, it makes sense...curly braces simply replace `/` as the delimiter, and `/` simply retains its non-specialness in regex.