#HTTP https://datatracker.ietf.org/doc/html/rfc7540#section-8.1.2 [[RFC7540]]に記載されている。 > Just as in HTTP/1.x, header field names are strings of ASCII characters that are compared in a case-insensitive fashion. However, header field names MUST be converted to lowercase prior to their encoding in HTTP/2. A request or response containing uppercase header field names MUST be treated as malformed (Section 8.1.2.6).