Read closer. "The characters '<' and '>' are unsafe because they are used as the delimiters around URLs in free text". The RFC itself uses "<URL:...>" because

Read closer. "The characters '<' and '>' are unsafe because they are used as the delimiters around URLs in free text". The RFC itself uses "<URL:...>" because it already uses "<...>" for BNF non-terminals, which are much more common than URLs in the RFC. Enjoy your undeserved upvote :)