If the context method for canvas returns null it means that the browser does not support canvas. The sub dom can be rendered in this scenario and can in fact be different for non-supporting user agents. Although I am very dubious that any device user agent will not be supporting the full HTML spec. going forward and expect to stay in business. Rich Schwerdtfeger CTO Accessibility Software Group From: Benjamin Hawkes-Lewis <bhawkeslewis@googlemail.com> To: Charles Pritchard <chuck@jumis.com> Cc: Frank Olivier <Frank.Olivier@microsoft.com>, Richard Schwerdtfeger/Austin/IBM@IBMUS, "Mike@w3.org" <Mike@w3.org>, "david.bolter@gmail.com" <david.bolter@gmail.com>, Cynthia Shelly <cyns@microsoft.com>, "public-canvas-api@w3.org" <public-canvas-api@w3.org>, "public-html-a11y@w3.org" <public-html-a11y@w3.org>, "public-html@w3.org" <public-html@w3.org> Date: 06/21/2011 01:21 AM Subject: Re: hit testing and retained graphics On Mon, Jun 20, 2011 at 5:07 PM, Charles Pritchard <chuck@jumis.com> wrote: > I've concerns about this approach. It would mean the sub-tree is no longer > separably viewable -- though not implemented at the moment, it is still an > option. I strongly agree that preventing the sub-tree being separably viewable is problematic, indeed to the point of it being a non-starter. The sub-tree was intended to act as an alternative for canvas like @alt is for "img". Making it nonsensical in complex cases would discourage UAs from making it viewable. This would prevent, for example, a user with at least some sight and images and canvas disabled from getting access to consistent text equivalents. This would break the specified use of "canvas" as a dynamic version of "img". > A clickable area is more like an SVG path, not a CSS box. Also true. -- Benjamin Hawkes-Lewis
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