Charm - Charisma - ENC/DRU/NEC

[commongood]

I apologize as this has no doubt been addressed (likely numerous times) in the past, but after dredging around the search function of this forum for a while now I gave up and decided to post this.

I would like some clarification on charming in EQ.

1) What checks are made each server tick that can cause charm to break? MR, level of charmer vs level of charmee and charisma? Anything else? What matters more?

2) What effect does charisma alone have on the likelihood of a charm break for an enchanter?

3) What about charisma for non-enchanter charmers like necromancers and druids? Does charisma matter here and if so is it to the same extent as with encs?