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http://lists.w3.org/Archives/Public/www-dom/2012OctDec/0061.html Right now relatedTarget is specced as being null on blur/focus. Why don't these just match focusout/focusin? Doing some spec archaeology, it looks like relatedTarget was specced as having the same value as target on blur/focus and then set to null in response to http://lists.w3.org/Archives/Public/www-dom/2010JanMar/0010.html. It seems to me that there's no downside to making relatedTarget do the same thing on focus/blur that is does on focusout/focusin respectively. From a web developers perspective, the only difference should be whether the event bubbles or not and whether it fires before/after focus has shifted. I know this is late in the cycle, but I just noticed this and this seems reasonable to include in the level 3 version of this spec.
Fixed in latest ED. relatedTarget for blur copied from focusout relatedTarget for focus copied from focusin (The bug says to "do the same thing on focus/blur that is does on focusout/focusin respectively", but I think that's reversed (or else I'm not understanding something).