Class used by some Kiwi Widgets that need to support mandatory input 
and validation features such as custom validation and data-type 
validation.
Mandatory support provides a way to warn the user when input is 
necessary. The validatation feature provides a way to check the data 
entered and to display information about what is wrong.
  | Method Summary | 
|  | get_background(self)Implement in subclass
 | 
|  | get_icon_window(self)Implement in subclass
 | 
|  | is_valid(self)Return true if the widget is in validated state
 | 
|  | set_blank(self)Changes the validation state to blank state, this only applies for 
mandatory widgets, draw an icon and set a tooltip
 | 
|  | set_invalid(self,
          text,
          fade)Changes the validation state to invalid.
 | 
|  | set_pixbuf(self,
          pixbuf)Implement in subclass
 | 
|  | set_tooltip(self,
          text)Implement in subclass
 | 
|  | set_valid(self)Changes the validation state to valid, which will remove icons and 
reset the background color
 | 
|  | update_background(self,
          color)Implement in subclass
 | 
|  | validate(self,
          force)Checks if the data is valid.
 | 
  | Inherited from ProxyWidgetMixin | 
|  | prop_set_data_type(self,
          data_type)Set the data type for the widget
 | 
| Must matche the data-type property. | read(self)Get the content of the widget.
 | 
|  | set_data_format(self,
          format) | 
|  | update(self,
          value) |