So there appears to be much confusion about how mentions should work and I think it comes from
* some clients implementing their own thing
* two nips around how to encode mentions in events
Events should either notify the mentioned or not. That's where the two standards differ.
If no notification is desired, the event.content should just contain the bech32 encoded reference.
If notification is desired, a tag should contain what is referenced and the event.content should only reference the respective tag.
When authoring TextNotes, the editor should not expect the user to know the difference. Opening a list of people when pressing the "@" symbol is convenient but does not mean that the symbol has to be part of the Note's serialization.
I would suggest to add some bell icon 🔔🔕 next to every reference which would allow the user to switch the notification on and off.
Advanced clients should allow notifications without references in the content.
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Ironically I do not know now if the references to four client devs above will trigger notifications as irisTo renders them as @npub