Does the Healing Bonus item property increase Healing Done, or Healing Received?

It's healing received

It is very ambiguously stated within the game, and the natural assumption would be that you give it to your healer to make their healing spells more effective. However, if you look at the item, "Belt of Bountiful Healing" it has the same, "Healing bonus: +15% Healing done" as fulvano's amulet. But the full description states:

While these belts provide no direct influence upon the injuries or fatigue of their wearers, the enchantments do lend additional power to those spells of mending and recuperation which strike it.

Clarifying that it affects incoming healing.

The bonus is on healing cast, not healing received.