This function converts an xs:string containing an IRI into a URI according to the rules spelled out in Section 3.1 of [RFC 3987]. It is idempotent but not invertible.

If $iri contains a character that is invalid in an IRI, such as the space character (see note below), the invalid character is replaced by its percent-encoded form as described in [RFC 3986] before the conversion is performed.

If $iri is the empty sequence, returns the zero-length string.

Since [RFC 3986] recommends that, for consistency, URI producers and normalizers should use uppercase hexadecimal digits for all percent-encodings, this function must always generate hexadecimal values using the upper-case letters A-F.

Notes:

This function does not check whether $iri is a legal IRI. It treats it as an xs:string and operates on the characters in the xs:string.

The following printable ASCII characters are invalid in an IRI: "<", ">", " " " (double quote), space, "{", "}", "|", "\", "^", and "`". Since these characters should not appear in an IRI, if they do appear in $iri they will be percent-encoded. In addition, characters outside the range x20-x126 will be percent-encoded because they are invalid in a URI.

Since this function does not escape the PERCENT SIGN "%" and this character is not allowed in data within a URI, users wishing to convert character strings, such as file names, that include "%" to a URI should manually escape "%" by replacing it with "%25".