The FLAT-BUTTON attribute must be set before the button is realized. The default value is FALSE.
Setting the FLAT-BUTTON attribute to TRUE forces the NO-FOCUS attribute to TRUE because the FLAT-BUTTON attribute only works with the NO-FOCUS attribute. Similarly, setting the NO-FOCUS attribute to FALSE forces the FLAT-BUTTON attribute to FALSE.
The mnemonic key (ALT accelerator) for a widget will not work if the NO-FOCUS attribute is TRUE because this removes the widget from the tab order. Also, because the widget is not in the tab order, pressing TAB will not change focus from the widget.