Help with Indexing on Grimoire

Would it be possible for someone to explain what it does? I did have a quick look around the forum, and on the grimoire 3.3 release and 3.8 but can't find it. I also saw it has been removed from 3.8? I use 3.3, and maybe 3.6 when I get the hang of it. So wanting to know what it is, and how to use it properly.

Indexes are used to either skip a part of the bot, or go back and make a loop.

An example:
explanation: First it will kill the enemy. Then it will check if the quest is not completed.
If it is indeed not completed yet. Then it will go up 2 indexes. Which means it goes back to kill.
This will repeat until the quest can be completed. And will then continue to the last part of the bot to complete the quest.

In grimoire 3.4 and later. Indexes aren't exactly removed, but rather Replaced with labels.

With labels, the same example as before will look like this: