- From: Carsten Bormann <cabo@tzi.org>
- Date: Tue, 14 Apr 2026 06:23:08 +0200
- To: Mike Bishop <mbishop@evequefou.be>
- Cc: HTTP Working Group <ietf-http-wg@w3.org>, "lrnregister@gmail.com" <lrnregister@gmail.com>
On Apr 14, 2026, at 06:07, Carsten Bormann <cabo@tzi.org> wrote:
>
> RFC 5234:
>
> NOTE:
>
> ABNF strings are case insensitive and the character set for these
> strings is US-ASCII.
I should have added more text from RFC 5234:
Hence:
rulename = "abc"
and:
rulename = "aBc"
will match "abc", "Abc", "aBc", "abC", "ABc", "aBC", "AbC", and
"ABC".
To specify a rule that is case sensitive, specify the characters
individually.
(Thinking the matching is case-sensitive is the most frequent misconception that I encounter when discussing ABNF.
I always include an extra ABNF comment when case-insensitive actually is intended (*); I probably should be using the otherwise redundant RFC 7405 %i more.
Ceterum censeo: This reminds me that STD 68 now needs to include RFC 7405 besides RFC 5234.)
Grüße, Carsten
(*) draft-ietf-cbor-edn-literals-21.txt:
HEXDIGA = "A" / "B" / "C" / "D" / "E" / "F"
; Note: double-quoted strings as in "A" are case-insensitive in ABNF
HEXDIG = DIGIT / HEXDIGA
Received on Tuesday, 14 April 2026 04:23:27 UTC