The P tag makes no sense to me

[Aspie96]

The P (uppercase!) tag makes no sense to me.

NIP-10 kind 1 notes within a thread typically contain a p tag for every user which has participated to or has been mentioned in that branch of the conversation. This will show as a notification to that user.

Conversely, NIP-22 kind 1111 comments contain a P tag for the author of the root and a p tag for the author of the parent, as well as every user mentioned in the comment.

The author of the root is already specified in the A or E tag (in the case of the I tag there won't be a P tag). So it is redundant when parsing the event. Indeed, if it were necessary, or even just useful, a specific tag for the author of the parent would be needed, but the p tag doesn't do this because it may also refer to a mentioned user.

I think it would be sensible for comments to behave similarly to replies to notes. I think there should be a p tag for the author of the root, of the parent and of middle comments in the thread, as well as for users mentioned in that thread. Those users would be notified and I think that's the correct behavior: it's the behavior of typical text notes, which is the most familiar one, it doesn't exactly lead to excessive engagement (Nostr doesn't really suffer from too many interactions) and it makes sense for the same reason it does for text notes.

[luigi1256]

The author of the root is already specified in the A or E tag

With the upper P tag, you can probably search all the comments on your photos, videos, articles

[vitorpamplona]

They have different use cases:

1. Filter by P if you want to notify your user of all replies to the thread.
2. Filter by p if you want to notify your user of only the immediate replies.

Some clients like option 1, others like option 2.

[Aspie96]

In this case, I suggest specifying that the p tags of the parent (which may be the root or another comment) should be copied as well, as with kind 1 notes.