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Re: Write-up about semantics in HTML5 from A List Apart

From: Ian Hickson <ian@hixie.ch>
Date: Wed, 7 Jan 2009 12:40:37 +0000 (UTC)
To: Julian Reschke <julian.reschke@gmx.de>
Cc: John Allsopp <john@westciv.com>, public-html@w3.org
Message-ID: <Pine.LNX.4.62.0901071231180.7181@hixie.dreamhostps.com>

On Wed, 7 Jan 2009, Julian Reschke wrote:
> Ian Hickson wrote:
> > ...
> > Thus there is no need for HTML5 to have author-usable features for
> > extensibility to solve the problems of decades from now. The extensibility
> > mechanisms for authors (and HMTL5 has many [1]) should solve _today's_
> > problems;
> 
> I'd prefer extensibility also to address future problem (at least to try 
> that), otherwise it's really a poor kind extensibility :-)

We can't possibly design an extension mechanism to address use cases, 
requirements, and problems that we know nothing about.


> > the language should be designed in such a way that the future 
> > maintainers of HTML can later extend the language to fix their 
> > problems. This is just how HTML4 was done; it's how CSS was done; it's 
> > how XML was done (you can't invent new XML syntax, for instance, that 
> > would require a new version of XML).
> 
> That is misleading. The important difference in XML is that the syntax 
> is frozen (-> no new parser required, at least in theory (*)), but 
> XML-based languages are extensible nevertheless (on the vocabulary 
> level, not the syntax level).

This is exactly what we have with HTML5. There are half a dozen or more 
extension mechanisms in HTML5, allowing you to extend all kinds of aspects 
of the language in ways that resolve problems we know about today. One of 
the things you cannot do, as with XML, is extend the syntax without 
changing the language.

(There are a number of things that XML can't do because of its limitations 
in extensibility. For example, authors can't extend it to represent 
non-tree structures, they can't extend it to have error recovery, they 
can't extend it it to have true multivalued-attributes, they can't extend 
it to allow them to correctly define validity in the face of namespaces, 
and they can't extend it to allow them to define validity for 
non-enumerated attribute values. This isn't a criticism of XML, it's just 
a description of the design choices made by the XML working group. It's 
normal for a language to have a constrained extensibility model.)

-- 
Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'
Received on Wednesday, 7 January 2009 12:41:13 UTC

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