RFC 3986

RFC 3986, titled "Uniform Resource Identifier (URI): Generic Syntax," was published in January 2005 by Tim Berners-Lee, Roy Fielding and Larry Masinter. It obsoletes RFC 2396 and the URL-specific portions of RFC 1738, and was promoted to STD 66, making it a full Internet Standard. The document defines the abstract grammar of a URI as `scheme:[//authority]path[?query][#fragment]`, where authority is `[userinfo@]host[:port]`. It specifies which characters are reserved (general delimiters `:/?#[]@` and sub-delimiters `!$&'()*+,;=`) and which are unreserved (`A-Z a-z 0-9 - . _ ~`), and it standardises Percent-Encoding as the way to represent any other byte. A major change from earlier specs is the recommendation that new schemes encode character data by converting to UTF-8 first and then percent-encoding each byte, addressing internationalisation concerns left open by the ASCII-centric RFC 1738. RFC 3986 also defines algorithms for parsing, normalising and resolving relative references, which is the foundation most server-side URL libraries still implement. Browsers, however, follow the parallel WHATWG URL Standard, whose parsing rules diverge in several places to match what real-world web content already does.