Fired when one of the editables gets focus.
Introduced by FocusObserver.
FocusObserver
Note that because FocusObserver is attached by the EditingView this event is available by default.
EditingView
args : tuple
module:engine/view/observer/focusobserver~ViewDocumentFocusEvent#args
name : 'focus'
module:engine/view/observer/focusobserver~ViewDocumentFocusEvent#name
object