Difference between seen_at and read_at?

[ibrahima]

Hi, I've got a simple question. What's the intended difference between seen_at and read_at? The readme mostly mentions read/mark_as_read. Is it like, one is for notifications having been delivered? But that doesn't quite make sense to me as seen. Would appreciate any clarification or examples of how people are using this, thanks!

On a tangentially related note, it seems like it'd be good to have indexes on these fields, because it seems like getting unread notifications would be a common operation.