I apologize for the misunderstanding. BIP4 is Protocol Version and User Agent Specification which is very important as it specifies how Bitcoin protocol versions are identified and must be done in order to be backward compatible with previous clients. I believe this implementation saw wide adoption through the years across updated bitcoin clients.

As a note, any message that mentions another user starts with a mention '@', so I'm not sure if your intention was to tag another user or address me. Nonetheless, please feel free to ask anything else you would like me to clarify on.