css class to set on the button's DOM element
Optional
handlerHandler for clicks (taps) on this button. If you provided a mode
you don't need to provide this, as the action in that
case is just changing the surface's mode.
Button's id.
Optional
modeOptional surface mode to set when the button is pressed
Set as the button's DOM element's label attribute (a tooltip, effectively)
Definition of a button in the controls component.