2483e263_TCL_TK_Command_Reference_Guide__Configure_Option
[Resource Name] indicatorOn [Resource Class] IndicatorOn [Description] Specifies whether the indicator should be drawn (default) or not. If false, the -relief option is ignored and the relief is set to sunken when widget is selected and raised in all other cases. [Configure Option] 
-indicatoron boolean
TCL/TK Command Reference Guide