What xp gains are affected by shrine of enlightenment?

After a little bit of research, the solution didn't turn out as I expected. First, here is how I tested it:

• For Quest-XP, I simply did the "Waiting for reinforcements" quest twice, on Nightmare Difficulty.
• For +XP per kill items, I rounded up Blood Clan Warriors with and without enlightement, as well as with and without +XP gear equipped
• For Massacre bonuses (I'm assuming that this is representative of other bonuses as well), I killed five Herald of Pestilence monsters and five Blood Clan Warriors with, and without enlightenment, as well as with, and without +XP gear two times to see the outcome.

The findings:

• None of the three things you listed had were influenced by +Enlightenment

This was weird. I was assuming that bonuses are not influenced, and that quests are not influenced, which turned out to be true. However, I assumed that +XP on items would influence it, but it did not. Specifically, the base XP I got on average from Blood Clan Warriors was exactly the same with and without +XP gear and Enlightenment on, meaning that it was the overall XP I got - the amount of +XP I got through my gear.

This means that the bonus XP seems to be calculated as:

totalXP = BaseXP + BaseXP * 0.25 + ItemXP

I think the reason they don't include Item bonus XP in the baseXP is that it would probably offer too much of an XP boost with high-level +experience helmet and gems on items, however this is speculation and something that only Blizzard can answer..