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Re: Production 21 (and others)

From: Dave Peterson <davep@acm.org>
Date: Thu, 30 Jan 1997 10:09:26 -0500
Message-Id: <v01540b02af1662d84975@[]>
To: w3c-sgml-wg@www10.w3.org
At 10:37 PM 1/29/97, lee@sq.com wrote:
>Dhris Maden wrote:
>> The regexp should bar *-- within a comment (and -- unless the TC
>> passes in time).  Even though, from XML's point of view, only *--> can
>> end a comment, these are still SGML comments, and *-- as comc would
>> still end the comment within the comment declaration.
>No.  Using *-- as COMC would require SGML comments to look like
><!*-- stuff *-->

Someone's getting confused here.  Until/unless the TC is adopted, there
is no such thing as COMC.  Using "*--" as COM would require....  If the
TC is adopted then there would be no COM, just COMO and COMC.  And XML
would use "--*" as COMO and "*--" as COMC.  The reference concrete syntax
(which only *must* be used in the SGML declaration) would use "--" as
both COMO and COMC.  SGML documents using the XML SGML declaration would
use comments that look like

        <!--* stuff *-->

except in the SGML declaration itself.

>Existing SGML systems will use -- to delimit comments, and it is pure
>happenstance (to them) that all XML comments start and end with an asterisk.

Only for documents whose SGML declaration specifies "--" for both COMO and
COMC.  Any robust SGML system should be able to switch concrete syntaxes
as specified in the SGML declaration, and any document whose SGML declaration
specifies "--*" for COMO and "*--" will not use "--" to delimit comments.

"Existing systems", presumably those that have not been updated to conform
to the TC, will not be able to read an SGML document (which includes its
SGML declaration) that is an XML document (which must use the XML SGML
declaration).  So to get an XML document into an "existing system", one
will have to change the SGML declaration to something that the existing
system can accept--but then it's no longer an XML SGML document, just an
"almost-XML" SGML document.

I'm not aware that anyone is expecting that, provided the TC is out in a
timely manner, one will expect XML documents to *always* go cleanly into
a system that doesn't implement the TC.  Otherwise, why bother with the
TC?  You'd be requiring all the odious restrictions and workarounds that
the TC is trying to eliminate.

Dave Peterson

Received on Thursday, 30 January 1997 10:11:32 UTC

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