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HTTP: The Definitive Guide

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Appendix A. URI Schemes

Many URI schemes have been defined, but few are in common use. Generally speaking, those URI schemes with associated RFCs are in more common use, though there are a few schemes that have been developed by leading software corporations (notably Netscape and Microsoft), but not formalized, that also are in wide use.

The W3C maintains a list of URI schemes, which you can view at:

The IANA also maintains a list of URL schemes, at:

Table A-1 informally describes some of the schemes that have been proposed and those that are in active use. Note that many of the approximately 90 schemes in the table are not widely used, and many are extinct.

Table A-1. URI schemes from the W3C registry





Netscape scheme to explore aspects of the browser. For example: about by itself is the same as choosing "About Communicator" from the Navigator Help menu, about:cache displays disk-cache statistics, and about:plugins displays information about configured plug-ins. Other browsers, such as Microsoft Internet Explorer, also use this scheme.


Application Configuration Access Protocol.



For file-sharing services using the Apple Filing Protocol (AFP) protocol, defined as part of the expired IETF draft-ietf-svrloc-afp-service-01.txt.


Reserved for future use by the Andrew File System.


Initiates a Microsoft NetMeeting conference session, ...

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