W3C home > Mailing lists > Public > public-html@w3.org > April 2007

Re: Version information

From: Ian Hickson <ian@hixie.ch>
Date: Sat, 7 Apr 2007 01:12:05 +0000 (UTC)
To: Elliott Sprehn <esprehn@gmail.com>, Chris Wilson <Chris.Wilson@microsoft.com>
Cc: "public-html@w3.org" <public-html@w3.org>
Message-ID: <Pine.LNX.4.62.0704070058480.5889@dhalsim.dreamhost.com>

On Fri, 6 Apr 2007, Elliott Sprehn wrote:
> This does not follow.
> In hundreds/thousands of years how will they know which version of HTML 
> they need to implement to view today's content?

They'll only have to implement the latest one. That's the whole point -- 
by strictly ensuring that all versions of HTML are, when designed, 
backwards-compatible with all prior content, any browser that implements 
HTML n+1 will automatically support any real content written for HTML n, 
for all values of n.

Look at it this way: today, how does a browser know what version of HTML 
to implement? They always implement HTML4, because if you implement HTML4 
you are automatically compatible with HTML 3.2 content, HTML2 content, and 
so forth.

Now, today this is complicated by a few factors:

 * The XHTML1 language *isn't* backwards compatible with HTML4, so 
   browsers have to implement both (or not do XHTML). The WHATWG specs
   go out of their way to define both HTML5 and XHTML5 as compatible 
   languages with minimal differences required to handle legacy content.

 * The quirks mode vs standards mode (vs almost standards mode, in the 
   browsers that correctly implement the CSS inline box model) means that
   for HTML4, browsers need to have three slightly different 
   implementations. The differences are relatively contained, however, and 
   this is independent of the HTML version number. HTML5 again goes out of 
   its way to limit the number of differences here (most are in CSS), 
   though there's still some work we can do (e.g. in handling of </br>).

> This is definitely a benefit of version information within the markup. 
> In the future when someone comes across a document with HTML they know 
> exactly which specification they need to implement.

If we do our job right, they'll only have to implement *one* version, the 
latest one, and it'll handle all content. In my opinion, the alternative, 
namely that they have to implement several dozen versions to handle 
content from several dozen years, is simply unworkable and unacceptable.

Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'
Received on Saturday, 7 April 2007 01:12:11 UTC

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