How to inspect Loki index key of boltdb

I’m trying to inspect index file like as chunks-inspect cmd.
But as far as I searched, I think there is no docs about index key format.

I show the boltdb inspection result to below

$ bbolt get keys --parse-format=ascii-encoded index



It looks like key is constructed from some fields it is separated by :.
First field is tenant id, second field is date, but I couldn’t figure out third and subsequent fields meant.
If you know reference (e.g. code references or docs), please tell me those.