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

Re: html 5 and accessibility issue - need of fallback content

From: James Graham <jg307@cam.ac.uk>
Date: Sun, 01 Jul 2007 17:26:07 +0100
Message-ID: <4687D59F.60208@cam.ac.uk>
To: Philip TAYLOR <Philip-and-LeKhanh@Royal-Tunbridge-Wells.Org>
Cc: Geoffrey Sneddon <foolistbar@googlemail.com>, public-html@w3.org

Philip TAYLOR wrote:
> Geoffrey Sneddon wrote:
>> What there is to stop that is that it is not compatible with what 
>> browsers currently do (the entire parsing algorithm is backwards 
>> compatible with current browsers — if it isn't, the spec needs to be 
>> fixed).
> "compatible with" /all/ "current browsers", or "compatible with"
> /some/ "current browsers" ?

"Compatible" in this case means "compatible enough with extant content 
that existing browsers can implement the spec without significantly 
degrading the site compatibility and hence web experience of their 
userbase". In practice this means reverse engineering what is done by 
browser engines with significant marketshare i.e. Trident, Gecko, Webkit 
and Presto. Where the behavior of these agree that behavior is specced 
as-is. Where there is disagreement a judgement call on the optimum 
behavior is made on a case-by-case basis taking into account whatever 
additional information about the pros and cons of each approach is 
available. If this judgment turns out to unsatisfactory for some reason 
(usually this will be that it turns out to be unimplementable without 
breaking significant amounts of existing content), the spec is changed 
to improve the behavior.

In the specific case of <embed>, introducing using a lookahead approach 
is undesirable because:
a) It is compatible with existing implementations (for example IE7 would 
render the "fallback" content in all cases

b) It is expensive to implement. In particular it breaks incremental 
rendering since the browser has to wait, possibly till the end of the 
file, to discover whether the markup following <embed> should be rendered

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-- ajs
Received on Sunday, 1 July 2007 16:26:15 UTC

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