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XML PE 157

From: John Cowan <cowan@ccil.org>
Date: Wed, 25 Oct 2006 12:16:34 -0400
To: public-xml-core-wg@w3.org
Message-ID: <20061025161634.GA18719@ccil.org>

(Well, it's simpler than I thought.)

Dieter Köhler <d.k@philo.de> writes
at <http://lists.w3.org/Archives/Public/xml-editor/2006JulSep/0007.html>:

> Appendix F.1 of the XML specs presents examples about how to
> automatically detect the encoding of an entity from the first
> characters of an XML encoding declaration without a byte order mark.
> These examples include UTF-16BE and UTF-16LE. However, section 4.3.3
> says that entities encoded in UTF-16 MUST begin with a byte order mark.

That is strictly limited to the UTF-16 encoding, and excludes the
related UTF-16LE and UTF-16BE encodings, in which BOMs are not present.
Note that "UTF16-LE" does not mean "UTF-16 encoding whose BOM shows it
to be little-endian" but rather "UTF-16-like encoding in little-endian
order without a BOM."  If U+FEFF appears at the beginning of a UTF-16LE
or UTF16-BE document, it is a ZWNBSP character (and therefore the document
cannot be well-formed XML), not a BOM.

> In the light of the examples it seems that the intention of the specs is
> to demand a UTF-16 byte order mark only when no XML declaration is used.
> Is this interpretation of the specs correct?

No.  If the encoding is UTF-16, a BOM is mandatory, whether or not an
XML declaration is present.

> If the answer is "no", I would suggest to remove the two incriminated
> examples from Appendix F.1 and to add an appropriate warning.

The examples are not in error, because they refer to the UTF-16LE and
UTF-16BE encodings rather than the UTF-16 encoding.

Core WG: Should we add specific references to UTF-16BE, UTF-16LE, CESU-8,
etc. etc. to 4.3.3?  If so, we might as well remove "We consider the
first case first" from Appendix F; it's more than obvious.

Where the wombat has walked,            John Cowan <cowan@ccil.org>
it will inevitably walk again.          http://www.ccil.org/~cowan
Received on Wednesday, 25 October 2006 16:17:47 UTC

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