|A Uniform Resource Identifier (URI) as defined by STD 66.
Objects using this TEXTUAL-CONVENTION MUST be in US-ASCII
encoding, and MUST be normalized as described by RFC 3986
Sections 6.2.1, 184.108.40.206, and 220.127.116.11. 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
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 this TEXTUAL-CONVENTION 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, for example when used
as an index field.
Where this TEXTUAL-CONVENTION is used for an index field,
it MUST be subtyped to restrict its length. There is an
absolute limit of 128 subids for an OID, and it is not
efficient to have OIDs whose length approaches this