You can use that attribute for dialogue that will only fire when the specific position is in use.
Example:
general:"Fuck my mouth!"{"check":{"atv_position":"==0"}}
general:"Fuck my tits!"{"check":{"atv_position":"==1"}}
general:"Fuck my pussy!"{"check":{"atv_position":"==2"}}
general:"Fuck my ass!"{"check":{"atv_position":"==3"}}
(0=oral, 1=tit, 2=vaginal, 3=anal, 4=other)
SO, if you are using an oral position, the mouth dialogue will be used, but none of the others.
If a vaginal position is used, the vaginal dialogue will be used, but not the others.
All animtools positions will have a "positiontype=X" within the text file.
If you want to check, just open the text file and search for that line.