The uri type represents a Uniform Resource Identifier
(URI) as defined by STD 66.
Objects using the uri type MUST be in US-ASCII encoding,
and MUST be normalized as described by RFC 3986 Sections
6.2.1, 6.2.2.1, and 6.2.2.2. All unnecessary
percent-encoding is removed, and all case-insensitive
characters are set to lowercase except for hexadecimal
digits, which are normalized to uppercase as described in
Section 6.2.2.1.
The purpose of this normalization is to help provide
unique URIs. Note that this normalization is not
sufficient to provide uniqueness. Two URIs that are
textually distinct after this normalization may still be
equivalent.
Objects using the uri type may restrict the schemes that
they permit. For example, 'data:' and 'urn:' schemes
might not be appropriate.
A zero-length URI is not a valid URI. This can be used to
express 'URI absent' where required.
In the value set and its semantics, this type is equivalent
to the Uri SMIv2 textual convention defined in RFC 5017.