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Proposal: Extend the encoding sniffing algorithm by adding a new, explicit step zero, like so: 0. If the document is an XML document, abort these steps. Justification. By extending the algorithm this way, then there is an *explicit* step to 'jump out of the algorithm if XML' - for which it would also be possible write test cases. Currently, and especially if the XML document lives in a 'nested browsing context'[1], then (unless there is a BOM) some browsers let the XML doc default to the encoding of the 'parent browsing context' instead of letting it default to the default encoding of the XML format (UTF-8). Webkit/Chromium/Opera have this error. Firefox do not have this error. I did not test IE9/10 yet, but suspect they are more on Firefox' side. Regarding defaulting to the encoding of the parent browsing context, then [see bug #foo and see bug #bar] More data in my related blog post.[2] [1] http://dev.w3.org/html5/spec/Overview#nested-browsing-context [2] http://målform.no/blog/white-spots-in-html5-s-encoding-sniffing-algorithm
Making this a higher priority to actively seek more feedback on from implementers and webdevs.
It seems like the current spec addresses this sufficiently. Quoting from https://mimesniff.spec.whatwg.org/#determining-the-computed-mime-type-of-a-resource : > 4. If the supplied MIME type is an XML type, the computed MIME type is the supplied MIME type. Abort these steps.
HTML5.1 Bugzilla Bug Triage: Fixed! Confirmed that W3C HTML links to [MIMESNIFF] which does indeed bailout fast for XML. If this resolution is not satisfactory, please copy the relevant bug details/proposal into a new issue at the W3C HTML5 Issue tracker: https://github.com/w3c/html/issues/new where it will be re-triaged. Thanks!