Adding specific damage

Effects that add damage to an already established damage profile should
do so using this phrase. You can add damage normally, which means
conditional on damage of that type already being dealt; or
unconditionally, which means that it should be dealt anyway. Heat
vulnerability -- which adds 2 damage when heat damage is being dealt --
should add 2 points of heat damage; while a curse that adds 2 heat
damage to any damage you get from any source should add the damage
unconditionally.
Multiplying damage

Including making up for rounding errors! E.g., a x50% and a x200%
condition will now always cancel each other out exactly.