The mapping for some existing standard and experimental protocols is outlined in the BNF syntax definition. Notes on particular protocols follow. The schemes covered are:
ftp File Transfer protocol http Hypertext Transfer Protocol gopher The Gopher protocol mailto Electronic mail address news USENET news nntp USENET news using NNTP access telnet Reference to interactive sessions wais Wide Area Information Servers file Host-specific file names prospero Prospero Directory Service
Other schemes may be specified by future specifications. Section 4 of this document describes how new schemes may be registered, and lists some scheme names that are under development.