163303e7_54_3__Event_types__Description
[Type] 9 [Name] FocusIn [Description] 
A widget got the input focus (see Section 53, “Focus: routing keyboard input” for a general introduction to input focus.) This can happen either in response to a user event (like using the tab key to move focus between widgets) or programmatically (for example, your program calls the .focus_set() on a widget).
54.3. Event types
Description