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Re: XML namespaces on the Web

From: Simon Pieters <simonp@opera.com>
Date: Thu, 19 Nov 2009 07:35:42 +0100
To: "John Cowan" <cowan@ccil.org>, "Lachlan Hunt" <lachlan.hunt@lachy.id.au>
Cc: "Liam Quin" <liam@w3.org>, public-html@w3.org, public-xml-core-wg@w3.org
Message-ID: <op.u3mpxsnyidj3kv@simon-pieterss-macbook.local>
On Wed, 18 Nov 2009 22:55:36 +0100, John Cowan <cowan@ccil.org> wrote:

> Lachlan Hunt scripsit:
>> The current XML5 proposal focusses entirely on the parsing issue,
>> leaving the definition of what's considered to be a conforming,
>> well-formed XML document to XML 1.0.  So, in this sense, it is fully
>> compatible with XML 1.0, and any conforming XML 1.0 parser will also be
>> a conforming XML5 parser, as the algorithm allows for either aborting or
>> applying the defined recovery procedure upon encountering a fatal error.
> This turns out not to be the case: the algorithm doesn't come close to
> XML 1.0 conformance.  For example, it accepts
>         <root less="<">
>         </root>
> without reporting a parse error, but this is not well-formed XML because
> it violates a well-formedness constraint.  In order to be an XML parser,
> it has to accept what an XML parser accepts, reject what an XML parser
> MUST reject, and report what an XML parser MUST report.  (In practice,
> XML parsers to be useful have to report many things that are not REQUIRED
> by XML 1.x, beginning with element names.)

Indeed, but it would be relatively easy to make the XML5 algorithm report  
an error for anything that is an error in XML 1.0.

> In addition, there are inputs like
>         this is not XML
> on which the XML5 algorithm fails to create a proper DOM, as there is
> no root element.

The DOM doesn't require a root element. For XML APIs that do require a  
root element, you could use the XML 1.0 behavior for this case and report  
a fatal error.

>> However, there have also been some suggestions to extend the list
>> of pre-defined entity references to all of those defined in HTML5
>> (which includes the XHTML and MathML sets).  If this were done, then
>> conforming XML 1.0 parsers would need to be updated to recognise these
>> entities in order to become conforming XML5 parsers.
> That would barely scratch the surface of the complications a parser
> would have to handle in order to conform to both XML 1.0 and XML5 even
> where they do not actually contradict one another.  (For example, the
> XML5 algorithm ignores the DTD internal subset, but XML 1.0 parsers MUST
> NOT do so until and unless they see a parameter-entity reference they
> do not recognize.

XML5 doesn't ignore the internal subset.

Simon Pieters
Opera Software
Received on Thursday, 19 November 2009 06:37:00 UTC

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