Examples for generating 'Stable, Predictable and Unique' keys

Reconciliation chapter spends a good time explaining why using the index or even Math.random() as a key is a bad idea, proceeding to suggest using an existent id as a key. When there's not an existent id, it's suggested to "add a new ID property to your model or hash some parts of the content to generate a key".

That's a very controversial issue, a lot of people do it wrong. An example of how to do it would make the chapter a lot better. It's an extensive chapter (compared to others) that seems to end up with no code conclusion. 

Start by reading the Reconciliation chapter's "Recursing On Children" section and the linked discussion about generating unique keys. Determine a clear, technically sound example for models without an existing id, then update that chapter with the example and explanation; done means the guidance addresses the common pitfalls without relying on unstable keys.