4. Do you have any security concerns related to this specification?

Maybe the XEP is not the place for this, but I would like clients to make it explicit that this is a "convenience" feature and not a a security one. Something like "consider anything you have sent (password, credit card number…) as now disclosed, retracting the message is not enough" (words are hard).

In the introduction is written:

"Due to the federated and extensible nature of XMPP it's not possible to remove a message with full certainty and a retraction can only be considered an unenforceable request for such removal. Clients which don't support message retraction are not obligated to enforce the request and people could have seen or copied the message contents already."

5. Is the specification accurate and clearly written?

Yes. I have a minor concern with Example 4 and its body "This person attempted to retract a previous message, but it's unsupported by your client.". I believe using a XEP-0428 fallback indication that the body is a fallback for XEP-0424, and setting this body to "/me retracted this message" is the way to go — this is how I implemented it in slidge. ;-)

In example 4 there is already a `<fallback>` element.

Concerning setting the body to "/me retracted this message", using `/me` is a nice touch, but the rest doesn't make sense to me, since that is not the message being retracted, but rather a previous one, and non-supporting clients have no way of knowing which one that was. So I think it can only be something like "/me retracted a previous message, but it's unsupported by your client."