I find the definition of idempotencyvalue in the grammar surprising: it looks like RFC 7230 quoted-string, but is actually just anything except for control char

I find the definition of idempotencyvalue in the grammar surprising: it looks like RFC 7230 quoted-string, but is actually just anything except for control characters, whitespace (!) and quotes, surrounded by quotes. Then I remember that the ETag header does the same thing since RFC 7232, where it used to use quoted-string with its escaping behaviour in RFC 2616. (And so they recommend avoiding backslashes because some recipients may mangle it.) Anyone have any idea why they’ve gone this way (ETag and Idempotency-Key), rather than using quoted-string? I will also note that people are already using a header named Idempotency-Key without quotes, e.g. https://stripe.com/docs/api/idempotent_requests https://stripe.com/docs/api/idempotent_requests. ETag has the “W/” indicator which requires some sort of disambiguation, but at least at this time I don’t feel Idempotency-Key needs quoting.