"Spell Damage Reduction" question

[Ashlebede]

When I look at that Spell Damage Reduction's ('AIsr') fields, I see these two fields :

Data - Damage Bonus
Data - Damage Reduction

Now, I know what the second one does ; it reduces the magic damage taken by the unit with that ability. However, what does the first one do? Does it increase the magic damage output or the magic damage taken? (Or is it just hardcoded and doesn't work right?)

Since I'm looking for a way to decrease/increase a unit's magic damage output without using Engineering upgrade and such...

 

[Weep]

It's an attack damage bonus, eg. if you set it to 10, a unit with the ability will show +10 attack damage.

How do I know? I just tried it myself. I always encourage people to try things themselves to learn.