That is, everywhere the hit shape would be drawn is considered a "touchable" part of the button.
swfbutton- addshape() adds the shape shape to this button. The following flags 'values are valid: SWFBUTTON_UP, SWFBUTTON_OVER, SWFBUTTON_DOWN or SWFBUTTON_HIT. SWFBUTTON_HIT isn't ever displayed, it defines the hit region for the button. That is, everywhere the hit shape would be drawn is considered a "touchable" part of the button.