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Re: HDP: Revised "Support Existing Content" Principle

From: Maciej Stachowiak <mjs@apple.com>
Date: Mon, 17 Sep 2007 20:07:30 -0700
Cc: "public-html@w3.org WG" <public-html@w3.org>
Message-Id: <99EBC209-32D5-4FA7-85C3-CA782772F099@apple.com>
To: Marghanita da Cruz <marghanita@ramin.com.au>


On Sep 17, 2007, at 7:24 PM, Marghanita da Cruz wrote:

> Maciej Stachowiak wrote:
>> On Sep 17, 2007, at 6:21 PM, Marghanita da Cruz wrote:
>>> To me, handling of poor markup by browsers is an example of
>>> the "Degrade Gracefully" Principle rather than the
>>> support existing content principle.
>> That's not the intent of the principle. "Degrade Gracefully" says  
>> nothing about the interaction of existing markup with either new or  
>> old browsers. It's all about new documents authored to conform to  
>> HTML5 being able to work reasonably in pre-HTML5 browsers.
>
> Sorry, but "Degrade Gracefully" is a concept that has been around as  
> long as the Web - the concept is that instead of providing an syntax  
> error the browser should attempt to interpret and display the content.

That concept is also referred to as error recovery and is covered by  
the "Handle Errors" principle.

> So, old browsers will most likely degrade gracefully rather than  
> report a syntax error, when they start seeing HTML5 code they do not  
> recognise.

They won't report a syntax error because browsers never report a  
syntax error. But they may fail in ways that are more serious or less  
serious. And the design of new features affects how bad the failure  
will be.

> There isn't much point in specifying what you want an old brower to  
> do with HTML5.

This principle is about new content that is designed to degrade  
gracefully in older browsers. It's not about specifying anything for  
behavior of old browsers - as you point out, it's too late to do  
anything about that. But the language can be designed to make it  
easier to create new content that works well in old browsers. The spec  
has conformance requirements for both implementations and documents,  
and this principle is mainly about document conformance.

Regards,
Maciej
Received on Tuesday, 18 September 2007 07:33:11 UTC

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