Mending seems to work about 2% of the time. I am trying to repair my mending pickaxe and I have 3 pieces of Mending armour, but they have full durability, my sword does not have mending, I have my pickaxe in my off hand, and I am getting 10 repair points after I get 5 levels of actual xp
When collecting XP orbs, game picks one of your armor pieces(if they have mending) first at random. If your armor is completely fixed, game picks one of the 2 items you hold in hands, if they also have mending.
N XP orbs with data
(Value:
M)
= N*M*2 mending repair points. (these values are directly proportional).So, for example, you're collecting 5 orbs with value of 2, you get 20 repair points.
(Tip: When you want to repair something, better take off your armor before getting XP.)