`<img>` fallback should not be prefetched #8

marcoscaceres opened this Issue Nov 2, 2012 · 2 comments


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Responsive Issues Community Group member

Currently fallback is being prefetched in the PreloadScanner. It should be ignored. See related implementation issue 5 for further discussion.

Responsive Issues Community Group member

Issue fixed in implementation.
@marcoscaceres - Do you want to explicitly state that in the specification?
IMO we would need an alternative fallback mechanism in any case, see #5


Yeah, I think it needs to be explicitly stated in the spec. If browsers downloads the image from the src attribute of the fallback img AND the src from the active source tag, it goes against the whole concept of responsive images, which is to prevent unnecessary downloads.

In my mind, the picture element would treat a nested img element the same as a noscript element treats nested img elements. If picture is natively supported by the browser, it should never download the fallback image src from the nested img element.

However, if a browser does not natively support the picture element, it would download the src from the nested img element inside the picture element.

I think this is clear to most CG members but should be ironed out in spec language.

@marcoscaceres marcoscaceres pushed a commit that closed this issue Dec 21, 2012
scottjehl This refactors the proposed markup (slightly) and picturefill JS to b…
…roaden browser support. The included update to README.md explains the changes I'm proposing to the markup pattern (there no changes to elements themselves) to support browsers that formerly did not work, like iOS4, IE browsers versions 6-10, Android browsers 1.x and up. As a result, there aren't any known "unsupported" browsers, in that every browser tested so far at least receives a fallback image - for example, IE6-8 will only see picture source elements that do not use media queries, since it doesn't support them natively (media types are ok though). Fixes #5 and Fixes #8.
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