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[Jsonpath] Re: RFC9839 and unicode chars to avoid

Carsten Bormann <cabo@tzi.org> Wed, 21 January 2026 20:56 UTC

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From: Carsten Bormann <cabo@tzi.org>
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Date: Wed, 21 Jan 2026 21:55:46 +0100
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References: <CAN+GtW08id-8xoENup+q569cgr7qy4nFXhRi3Una_Up-bCBjFQ@mail.gmail.com> <41395C71-3320-4510-B4BE-795C14A847A4@saxonica.com> <CAN+GtW2eR344z9H_dVXcXOTMF5LCHo6JpjJOhYguD2rF8e7w5w@mail.gmail.com> <CANH0GbJxqq6Aq=yu9VF03=N5--f8dO-k+4OZOEW4fjyGnYeVkg@mail.gmail.com> <CAHBU6isK1Nad4nak8=7GqnOr3wWTs+NyRoCLWB-soY6GB0oyxQ@mail.gmail.com>
To: Tim Bray <tbray@textuality.com>
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CC: Glyn Normington <glyn.normington.work@gmail.com>, Michael Kay <mike@saxonica.com>, jsonpath@ietf.org, Alan Painter <alan.painter@gmail.com>
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Subject: [Jsonpath] Re: RFC9839 and unicode chars to avoid
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Hi Tim,

> On Jan 21, 2026, at 19:33, Tim Bray <tbray@textuality.com> wrote:
> 
> Well, 9839 aside, my reading of RFC 8259 is that U+0000 isn’t a legal character in JSON member names or string values, see https://datatracker.ietf.org/doc/html/rfc8259#section-7 - so one would think that if it appears in a test suite, that particular test case should fail, no? And that such a test would be valuable?

I’m not sure I understand what you are trying to say here.
JSON of course can represent any Unicode string (and a few non-Unicode strings, but RFC 9535 is careful to limit itself to sequences of Unicode scalar values).

Section 7 of RFC 8259 defines the string literals that can be used in a JSON text to represent strings as JSON values.
Wisely, (the original) JavaScript does not allow C0 control characters in string literals, and JSON follows this.
But you can have your null byte in a string, represented in the JSON text as \u0000.

Maybe I’m completely missing what you are talking about…

Grüße, Carsten

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