- * some kind of sorted type, example:
- ZADD mykey foo 100
- ZADD mykey bar 50
- ZRANGE mykey 0 1 => bar foo
- This is able to take elements sorted because a binary tree is used to store
- the elements by 'score', with the actual value being the key. On the other
- side the type also takes an hash table with key->score mapping, so that when
- there is an update we lookup the current score and can traverse the tree.