Download the definition.
(right click and save target as)
Some nice people over in Spain (Laboratorio de Arquitectura y Computación) have made a nifty video detailing on how to use the thing:
Source code of the Vornoi2D node.
Have fun, and drop a line if something isn’t working the way it should (take care to select the boundary points in order – clockwise or trigonometric – doesn’t really matter).