To be a bit more clear than the title, I'm looking for something similar to how it works on World of Warcraft, where, for example, a Warrior's Sunder Armor reduces enemy armor by 4%, and stacks up to 3 times to drop it by 12%.
Example: a spell that inflicts poison, say the poison does 15 damage per turn for 5 turns. add the chance for it to stack on itself on the next turn if it afflicts the poison again when you use the ability, it'll show the poison icon with a 2 over it, then the enemy then suffers 30 damage per turn.
Additionally, if possible, I'd like it to (under normal circumstances) expire 1 stack at a time, if applied that way. Example: you apply 1 stack of poison on turn 1. you then apply another stack on turn 2. the first application expires on turn 5, while the 2nd doesn't expire until turn 6.
Also, probably through use of an additional notebox tag, I'd like to also be able to have new applications refresh the duration. Example: Poison is inflicted on turn 1, since it'd expire on turn 5, you re-apply it on turn 4, causing it to expire instead on turn 9, but also adding another stack.
As usual, I'd prefer everything be written to use through note tags. Examples: Place <stack> in states you want to be able to stack on itself. Place <stack refresh> on ones you want to refresh per application.
And before I forget, please write it in a manner to where the stack cap is determined in the note tag, Ex: <stack 10>