@sirflimflam
I think it is loosly explained.
If I remember correctly, "heal" just means to alter in a specific way. Whether something is considered healed or broken is up to the individual's judgement. In other words, it is called healing because it can be altered back to an ideal/origional state which has been agreed upon to be good. Now if what you think is healed and what I think is healed are different, then whoever is doing the "fixing" gets the say.
Say you were to snap a bone in half. It will heal over time reguardless of what we do (unless it gets infected/ other complications arise). However, we can shape how it heals to properly fix it with a cast and surgery (if needed). Same for him except with magic.
He can "heal" your body to look differently, as long as it is on a physjcal level. He cant seem to alter someone on a chemical level. So he can "heal" you a pair of breasts, but not on the genetic level. The most he can do in terms of actual healing is quicken natural regeneration. He just dictates where and in what way you renegerate.