"URI Templates are strings that contain embedded variables that are transformed into URIs after embedded variables are substituted. This specification defines the structure and syntax of URI Templates."

"This page allows the user to test the effect of various string functions used in URI creation, processing, or interpretation. Its initial intention is to help debug the atomic pieces of what will become more elaborate processing routines, but it may also be helpful in exploring the consequences of various design decisions in URI-related specifications."

A lot of this document is focused on how AJAX applications are making use of the fragment identifier.

IETF draft for spec'ing out the about: URI scheme.

"known" uri schemes...

"In this case, the ampersand ends up in the string as a plain ampersand. But when the time comes to set the document location, IE applies another entity replacement, while other browsers don't. In IE 6, this code results in a visit to a URL with a copyright symbol in it."

"This is primarily the fault of delicious, which associates comments with pages based on the MD5 hash of their url. Add a trailing slash and the hash changes. Change the hostname, and the hash changes. (Of course, delicious just changed their hostname and thus broke all meta-commentary. Sigh.)"

Boeing uses XRIs to fully qualify identifiers and avoid name collisions between employee IDs, application IDs, device IDs, IDs received in SAML (Security Assertion Markup Language) assertions from business partners, etc.