Re: 23.0.60; [nxml] BOM and utf-8

[Patrick Drechsler <patrick@pdrechsler.de>]

Patrick Drechsler <patrick@pdrechsler.de> writes:

> mah@everybody.org (Mark A. Hershberger) writes:
>
>> Patrick Drechsler <patrick@pdrechsler.de> writes:
>>
>>> is the attached xml file (simple.xml) really invalid (as indicated by
>>> nxhtml) or is this a bug in nxhtml?
>
> s/nxhtml/nxml/
>
>> The file simple.xml is really invalid.
>>
>> http://www.w3.org/TR/2006/REC-xml-20060816/#sec-prolog-dtd
>>
>> The XML spec gives the following syntax description for the prolog of an
>> XML file (I've only copied the relevant parts):
>>
>>     [3]    S	    ::=  (#x20 | #x9 | #xD | #xA)+
>>     [22]   prolog   ::=  XMLDecl? Misc* (doctypedecl  Misc*)?
>>     [23]   XMLDecl  ::= '<?xml' VersionInfo EncodingDecl? SDDecl? S? '?>'
>>
>> Note that there is no S before the literal “<?xml" and that "<?xml" is
>> optional.
>>
>> So, yes, an file that contains whitespace before "<?xml" is invalid XML.
>
> Finally having some spare time I read the specs from above and I have a
> followup question concerning your last sentence:
>
> The BOM in my example file is not whitespace, it is xEF xBB xBF (it is
> only displayed as whitespace by Emacs). According to the W3C site this
> is valid:
>
> ,----[ http://www.w3.org/TR/2006/REC-xml-20060816/#charencoding ]
> | Entities encoded in UTF-16 MUST and entities encoded in UTF-8 MAY
> | begin with the Byte Order Mark described by Annex H of [ISO/IEC
> | 10646:2000], section 2.4 of [Unicode], and section 2.7 of [Unicode3]
> | (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.
> `----
>
> Also http://www.w3.org/TR/2006/REC-xml-20060816/#sec-guessing-no-ext-info

sorry, wrong link: http://www.w3.org/TR/2006/REC-xml-20060816/#sec-guessing

> and
>
> ,----[ http://www.w3.org/TR/2006/REC-xml-20060816/#sec-guessing-with-ext-info ]
> | If an XML entity is in a file, the Byte-Order Mark and encoding
> | declaration are used (if present) to determine the character encoding.
> `----
>
> sound like a BOM is a legal (although optional) part of a xml file coded
> in utf-8.
>
> But I am not an expert, so please correct my potentially incorrect
> interpretation.
>
> In case my interpretation is correct, this is a bug in emacs' nxml mode.
>
> Cheers,
>
> Patrick 

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