Life Drain / Drain Life: Works on Undead &...?

[tinkthank]

This question has been asked before, but my searches reveal contradictory statements. I'd like to try to find some sort of definitive answer to the following questions:

1. Is Life Drain / Drain Life functionally identical but with two different names? Or are they somehow different, and if so, how?

2. I *think* I have seen commanders equipped with a Wraith Sword or similar gain hitpoints when hitting undead enemies. Thus it seems that Life Draining also works on Undead. Can this be corroborated or falsified by an "Authority"?

3. I thought Undead were lifeless. Maybe not. In any case, however question #2 is answered: Will Life Drain work on those flagged "Lifeless"?

4. Some items (such as the Wraith Sword) cast "Drain Life" automatically when you hit with a melee weapon. Others allow you to cast the spell "Drain Life" (or Life Drain?), such as the Standard of the Damned. Is there a big difference here in the way the spells work?

Thanks much.