I posted this over on the Roll20 support forums but I figured I'd ask here as well.
Basically I want to incorporate bonus damage dice in my attack macros. Right now I've got this line:
/roll 2d20k1+10 /roll 1d12+8
For one of my Avenger's attacks. basically I want to incorporate that 1d6, but only have it rolled and added to the attack damage total if the higher of the two d20s is a 20. I'm not sure how to do that (or if such a feature has really been implemented) and the built in exploding dice feature /roll 4d6! for example adds another die to the first roll of the same type on a crit, but doesn't seem to over any other application.