Given the history below, would it be sensible to accept BOMs for UTF-8
encoding, but not for UTF-16 and UTF-32? In other words, are BOMs needed
and/or used in the wild for UTF-16 and UTF-32?
Maybe the text can say something like "SHOULD accept BOMs for UTF-8, and MAY
accept BOMs for UTF-16 and / or UTF-32"?
Thanks,
Pete Cordell
Codalogic Ltd
C++ tools for C++ programmers, http://codalogic.com
Read & write XML in C++, http://www.xml2cpp.com
----- Original Message -----
From: ""Martin J. Dürst"" <duerst(_at_)it(_dot_)aoyama(_dot_)ac(_dot_)jp>
To: "Henry S. Thompson" <ht(_at_)inf(_dot_)ed(_dot_)ac(_dot_)uk>
Cc: "John Cowan" <cowan(_at_)mercury(_dot_)ccil(_dot_)org>; "IETF Discussion"
<ietf(_at_)ietf(_dot_)org>; "Paul Hoffman" <paul(_dot_)hoffman(_at_)vpnc(_dot_)org>;
"JSON WG"
<json(_at_)ietf(_dot_)org>; "Joe Hildebrand (jhildebr)"
<jhildebr(_at_)cisco(_dot_)com>; "Anne van
Kesteren" <annevk(_at_)annevk(_dot_)nl>; <www-tag(_at_)w3(_dot_)org>;
"es-discuss"
<es-discuss(_at_)mozilla(_dot_)org>
Sent: Thursday, November 14, 2013 11:14 AM
Subject: Re: [Json] JSON: remove gap between Ecma-404 and IETF draft
Hello Henry, others,
On 2013/11/14 18:44, Henry S. Thompson wrote:
John Cowan writes:
Joe Hildebrand (jhildebr) scripsit:
If 404 doesn't allow [a BOM], I don't see a strong need to add it.
Parsers can always be more forgiving of what they will parse than what
the spec says, particularly since section 9 says "A JSON parser MAY
accept non-JSON forms or extensions".
It's not clear that 404 disallows it, since 404 is defined in terms of
characters, and a BOM is not a character but an out-of-band signal.
I think this is a crucial observation.
Yes, and I think it's based on the experience with XML. But while this
experience may be applicable to JSON, Anne's original comment about the
BOM and XMLHttpRequest suggests that 404 actually currently does not
tolerate a BOM, and that implementations (except for XMLHttpRequest) also
don't.
To give some historic background, the BOM for UTF-8 wasn't in the first
edition of XML (http://www.w3.org/TR/1998/REC-xml-19980210#sec-guessing).
It only later came in because Microsoft used it for notepad to be able to
quickly distinguish between UTF-8 and the legacy system encoding. Because
many people were writing some XML by hand, and some of them were using
notepad, the pressure on XML to accept a BOM at the start of an UTF-8 file
mounted, and it was included in the second edition of the XML
Recommendation (http://www.w3.org/TR/2000/REC-xml-20001006#sec-guessing).
Compared to XML, JSON may be much less edited by hand, or much less edited
on notepad, or otherwise just have a different history from XML, but we
have to make sure.
Regards, Martin.
I note that XML approaches
this problem in what might be a useful way. The XML ABNF makes no
mention of BOM, it's not part of any XML document as such. But it
_is_ allowed. The relevant wording [1] is:
Entities ... may begin with the Byte Order Mark described by Annex H
of [ISO/IEC 10646:2000], section 16.8 of [Unicode] (the ZERO WIDTH
NO-BREAK SPACE character, #xFEFF). _This is an encoding signature,_
_not part of either the markup or the character data of the XML_
_document._ XML processors must be able to use this character to
differentiate between UTF-8 and UTF-16 encoded documents. [emphasis
added]
ht
[1] http://www.w3.org/TR/REC-xml/#charencoding
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