The `event-focus` module supplies a behavior patch for the native `focus` and `blur` events to allow them to bubble for event delegation.
Most DOM events bubble. If, for example, you click on a button in a form, the click event will be dispatched to event subscribers on the button, on the fieldset, on the form, on the div containing the form, and so on up to the `document`. You can subscribe to the click event at any level and your callback will be executed. But `focus` and `blur` aren't like that. They are only dispatched to subscribers on the element that received or lost focus.
But we like event delegation so we determined a way to synthesize bubbling for `focus` and `blur` using capture phase subscriptions in non-IE browsers, and proprietary focus-related events in IE that do bubble. The result should be transparent for individual element `focus` and `blur` subscriptions, but make `focus` and `blur` work as you would expect when subscribing higher in the document tree.
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