<World-Wide Web> (URL) (Previously "Universal"). A draft standard for specifying an object on the Internet, such as a file or newsgroup. URLs are used extensively on the World-Wide Web. They are used in HTML documents to specify the target of a hyperlink.
Here are some example URLs:
ftp://wuarchive.wustl.edu/mirrors/msdos/graphics/gifkit.zip ftp://spy:secret@ftp.acme.com/pub/topsecret/weapon.tgz http://www.w3.org/default.html news:alt.hypertext telnet://dra.com mailto:dbh@doc.ic.ac.uk http://wombat.doc.ic.ac.uk/?Uniform+Resource+Locator http://www.w3.org/default.html#IntroductionThe part before the first colon specifies the access scheme or protocol. The part after the colon is interpreted according to the access scheme. In general, two slashes after the colon introduce a hostname (host:port is also valid, or for FTP user:passwd@host or user@host). Schemes include: ftp, http (World-Wide Web), gopher or WAIS. The "file" scheme should only be used to refer to a file on the same host but is often used incorrectly as a synonym for ftp. Other less commonly used schemes include news, telnet or mailto (e-mail). The port number can generally be omitted from the URL and will default to port 80. The last (optional) part of the URL may be a query string preceded by "?" or a "fragment identifier" preceded by "#". The later indicates a particular position within the specified document.
Only alphanumerics, reserved characters (:/?#"<>%+) used for their reserved purposes and "$", "-", "_", ".", "&", "+" are safe and may be transmitted unencoded. Other characters are encoded as a "%" followed by two hexadecimal digits. Space may also be encoded as "+".
The authoritative URL specification from CERN.
(25 Nov 1996)