This is an archived snapshot of W3C's public bugzilla bug tracker, decommissioned in April 2019. Please see the home page for more details.
https://w3c.github.io/uievents/#event-type-keydown defines Event.target as "focused element processing the key event or if no element focused, then the body element if available, otherwise the root element". However, "the body element" and "the root element" aren't uniquely defined within a UA. The UA may have multiple browsing contexts, and each browsing context can contain multiple documents.
Now tracking as: https://github.com/w3c/uievents/issues/52