I always thought that positive energy is harmful to undead and negative energy heals them, but I recently found out that, technically at least, undead by default are only healed by negative energy, and nothing in their type description says that positive energy harms them.
This is supported by the fact that every positive energy based heal (or cure) spell in the core manual has to specify that it deals damage to undead.
I then started wondering if somewhere in the books is a positive energy based spell, supernatural ability, spell-like or whatnot ever described as healing undead?
I'm referring to 3.5e's rules because that is the only edition I've ever played, but if this interaction is true in any other edition or Pathfinder, I'm still interested.
And obviusly I'm talking about healing your average zombie or smarter types of typical undead. I'm not talking about particular creature like the deathless from Eberron.