Remark: My question is NOT about Style Setting Install Key.
It is about single Option Install Key in Drop-Down Setting.
Say, I setup a drop-down setting "Header color" with Setting Install Key "header-color" and two options: "Dark" and "Light".
Each option have color value in Code field which will be placed instead of /*[[header-color]]*/ placeholder. That is clear.
But beside it each option have an own Install Key field. What is the purpose of these keys? And how they can be used?