ArangoDB: how to pick a right index

Question

I'm using ArangoDB and it offers several types of index (Persistant, Hash, Skiplist, Geo, Fulltext) which seem to work in different ways.

In addition to those options, some of them allow users to define additional parameters.

I understand what Unique index and Duplicate index would do. However I don't understand,

1. The difference between the 5 index types.
2. What Sparse index does

Answer 1

There is quiet an exhaustive page on the terminology and the corresponding technology of ArangoDB indexes:

https://docs.arangodb.com/3.4/Manual/Indexing/IndexBasics.html

In case some questions are still left, comment and I'd expand on the answer. But the page does have all answers to the above questions.