alt Hacker NewsThe relevant word here is MAY[1]
It's true that if an API requires the devs of its consumers to have consulted documentation in order to respect the RateLimit header, they can just as easily include custom API logic for traffic control, but this does provide a nice standardized way to do so nevertheless.
And since the word is "MAY", APIs may also use standard responses that don't require an custom handling. As an example a CLI-builder library which parses OpenAPI spec can adopt changes to handle the RateLimit header automatically, in the situations where consulting docs is not required.