Valid characters for URI schemes?

Question

I was thinking about Registering an Application to a URL Protocol and I\'d like to know, what characters are allowed in a scheme?

Some examples:

• h323

Answer 1

According to RFC 2396, Appendix A:

  scheme        = alpha *( alpha | digit | "+" | "-" | "." )

Meaning:

The scheme should start with a letter (upper or lower case), and can contains letters (still upper and lower case), number, "+", "-" and ".".

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Note: in the case of

paparazzi:http:[//[:[][]]/

the scheme is only the "paparazzi" part.