Proper now, there are collections in Ordinals marketplaces.
For instance:

• https://openordex.org/collections
• https://ordinalswallet.com/collections
• https://ordswap.io/collections/

However I failed to seek out the assortment associated params within the Ordinals’ docs

So my questions are:

1. The place are "collections" saved? Are in addition they saved on chain? or they’re simply listed off chain?
2. If on chain, how you can write "metadata"-like information to specify the collections? What’s the format?
3. If off chain, are they listed by creators or marketplaces, or each? How these indexes are handed/aligned throughout marketplaces?