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http://heycam.github.io/webidl/#common-BufferSource [[ typedef (ArrayBufferData or ArrayBuffer) BufferSource; ]] That should say ArrayBufferView, not ArrayBufferData, as far as I can tell. Spotted by David Dorwin in bug 23369 comment 49.
https://github.com/heycam/webidl/commit/f0b87bd744856b11e7d358398e46196f8a4c76f6