its looking for "imeta" tags first, then guessing on the URLs in the content. if the URL ends with a 64 length hex string it guesses that its a blossom compatible URL and tries to copy it
worst case it fails and the user isn't any worse off
Discussion
Can't we just specify a ping to the server that all blossom servers can reply with ack + the filetypes they support?
I'd like to avoid adding any "meta" endpoints to blossom servers, since that introduces and extra step for clients to intact with them and then the client needs to ask the server how to interact with it before it tries... things get messy
The /mirror endpoints works kind of similar though. the client makes a PUT /mirror request with the url and sha256 of the blob the user wants to mirror, then the server either mirrors it and returns 200 or refuses and returns 400 or 401