Dan Connolly at the W3C keeps a very comprehensive list of URI schemes.
IANA*, however, has the official list.
One that I haven't seen documented, however is the aim: scheme.
Creating new URI schemes is bad for several reasons. A practical one, however, is the difficulty of using them with standard tools. Everytime you create a new scheme, tools like parsers, etc. must be taught how to use this.
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