ActionScript for Flash MX: The Definitive Guide, 2nd Edition By Colin Moock
Chapter 18. ActionScript Language Reference
Button._xmouse Property
Flash 6
horizontal location of mouse pointer, relative to the button's registration point
read-only
theButton._xmouse
Description
The floating-point _xmouse property indicates the horizontal location of the mouse pointer's hotspot, relative to theButton's registration point. To obtain a consistent _xmouse coordinate that is always measured relative to the Stage, use _root._xmouse.