Runed Bracers

Hey guys. I was messing around with my map making items for it. I went into the item abilities and began editing the spell for runed bracers (called spell reduction or something). Anyway, as I was editing I stumbled upon an editable field above the "damage reduction" field called "damage increase". I took this to be one of two things: Damage increase (normal damage) or spell damage dealt increase. I was hoping for the latter. I tried it and tested, and apparently it does neither. Does anyone know what it DOES do? It would be very helpful.

If you put damage increase on, then when you wear the bracers, u will take increased damage from spells, i would guess.

don't you think that would make no sense since you could just put a negative value in the reduction field?