Question: Make unit type unable to attack other unit type

[Rainther]

Hi,

I want to make Zerglings unable to attack Planetary Fortress, to ignore it as if it were invincible.
How could I do this? I bet it has something to do with Data -> Validators, but I can't get my head around how that works.

 

[Rainther]

Bumpish

 

[Rainther]

Bump.

Does anybuddy know a good way of achieving this?
There are some Filter I could use, but I'd prefer to make a specific unit type unable attack nor care for an other unit type.