It has both, but so does the Light. They're bound to each other-- neither exists without the other, and both are equally responsible for creation.

The Void is the stronger of the two, magically speaking, but it can't heal the way the Light can. Not in the same way. [he considers a moment, thinking.] For example, I can heal myself through leeching an enemy's life, and I could normally save someone else with shadow magic. Theoretically. But I would have to twist our life forces and exchange them, so it's highly unlikely.