public int getTabUnderlinePlacement() {
		return getClientPropertyInt( TAB_BUTTON_UNDERLINE_PLACEMENT, BOTTOM );
	}
Returns placement of underline if toggle button type is {@link ButtonType#tab}.
If underline placement is not specified, returns {@link #BOTTOM} as the default
value.

@since 2.3
flatlaf-extras/src/main/java/com/formdev/flatlaf/extras/components/FlatToggleButton.java