Web authors need a way to detect whether or not different canvas contexts are supported. Currently authors do this by calling <canvas>.getContext, but this can be very expensive.
Dean proposed adding a supportsContext method in http://lists.w3.org/Archives/Public/public-html/2012Sep/0119.html
Ian added <canvas>.supportsContext in r7482 of the WHATWG spec:
The work to implement <canvas>.supportsContext in WebKit is being tracked in
We should consider pulling this in for HTML5.
Assigning to Silvia since the change has been made on the WHATWG side of things.
See also https://github.com/w3c/html/commit/90c0786311cd92d5a4fd1c546e6a8a766c6d3b2c
staged in https://github.com/w3c/html/compare/master...feature;whatwg_patches_week43_2012
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Rationale: adopted resolution by WHATWG