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   Re: ATTN: Please comment on XHTML (before it's too late)

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  • From: Paul Prescod <paul@prescod.net>
  • To: xml-dev <xml-dev@ic.ac.uk>
  • Date: Sun, 29 Aug 1999 18:09:51 -0400

David Megginson wrote:
> I agree that there needs to be some sort of versioning available -- it
> could be an html:version attribute (the best solution, I think), or
> perhaps just the version of the DTD used in the DOCTYPE declaration
> (much messier).

Can you specify an algorithm for determining when you have a new version
vs. a new language? I can: you have a new language when instances can
break conforming software. Instances can break conforming software as
soon as you add an element or broaden the definition of an attribute.

> I think that Namespaces are the wrong tool to use for versioning,
> because using them that way makes easy, typical jobs much harder, and
> that's just bad design.

You keep repeating that it makes your life so much harder but what would
be so brutal about standardizing and recognizing an equivalence
declaration? For HTML's simple idea of equivalence, it would be trivial.

> Fortunately, XML isn't source code (or compiled code), so we don't
> have the same problem 

We have exactly the same problem. Assumptions about the form of the
input may cease to be valid when the input's version number shifts. Only
the people making the new version (or documents conforming to the new
version) know whether it is safe to treat the new documents as old ones.
**You cannot write software today that is guaranteed to be compatible
with HTML 6.**

> -- I was using that example only to demonstrate
> that once there's software deployed that recognizes a certain set of
> XHTML Namespaces (preferably a set with one member), it will be very
> difficult to introduce any new Namespaces.

Not with an equivalence mechanism.

> They already have the mechanism: if you see an unknown attribute,
> ignore it; if you see an unknown element, ignore its start and end
> tags and process the content.  It's not elegant, but it's workable.

That doesn't work. The introduction of APPLET allowed paragraphs within
paragraphs. Is it so far fetched that this could crash a
standards-conformant application? What's the point of being standards
conformant if you can't rely on any of the rules that you programmed
your application to use. 

This, to me, is the crux of the issue. We have a responsibility as
standardizers to implementors.

> That said, as I mentioned above, I agree that some sort of versioning
> is needed -- the three-Namespace approach just seems equivalent to
> amputating my leg to get rid of a wart.

There is no amputation required. Yes we have some work to do in defining
the equivalence mechanism -- but we always had that work ahead of us.
Yes there is some effort required in implementing it -- but that effort
was going to be required regardless.

 Paul Prescod

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