modifier descriptions with updating values
i often see modifiers that have updating descriptions, like slarks essence shift for example. the description of the modifier says something like "stealing X agility", with the X value changing depending on the number of stacks. how can i do the same thing in my modifiers?
ive tried to look at other customs for examples, but what ive found confuses me and i cant copy what they do. ive seen things like %value%, %value%%%, and %value%d. but i dont understand what the differences between these are, or how to use them.
can someone explain how to do this? it would be greatly appreciated!