1 Focus

     2 =====

     3 

     4 Only one non-container widget can have focus at the time.

     5 All parent containers also have focus.

     6 

     7 Events emitted on change: focus, unfocus

     8 

     9 mousedown - focus widget under mouse or its parent if canfocus() == false

    10 

    11 tab - focus next child in container

    12 shift-tab - previous child

    13 

    14 hide() -> unfocus