Editing Uniform Resource Name (section)

==Syntax==
The syntax of a <code>urn:</code> scheme URI is represented in the [[augmented Backus–Naur form]] as:{{sfnp|RFC 3986|2005}}{{sfnp|RFC 8141, section 2|2017}}

<syntaxhighlight lang="abnf">
namestring    = assigned-name
                [ rq-components ]
                [ "#" f-component ]
assigned-name = "urn" ":" NID ":" NSS
NID           = (alphanum) 0*30(ldh) (alphanum)
ldh           = alphanum / "-"
NSS           = pchar *(pchar / "/")
rq-components = [ "?+" r-component ]
                [ "?=" q-component ]
r-component   = pchar *( pchar / "/" / "?" )
q-component   = pchar *( pchar / "/" / "?" )
f-component   = fragment

; general URI syntax rules (RFC3986)
fragment      = *( pchar / "/" / "?" )
pchar         = unreserved / pct-encoded / sub-delims / ":" / "@"
pct-encoded   = "%" HEXDIG HEXDIG
unreserved    = ALPHA / DIGIT / "-" / "." / "_" / "~"
sub-delims    = "!" / "$" / "&" / "'" / "(" / ")" / "*" / "+" / "," / ";" / "="

alphanum      = ALPHA / DIGIT  ; obsolete, usage is deprecated
</syntaxhighlight>

or, in the form of a [[syntax diagram]], as:

[[File:URN_syntax_diagram_-_namestring.png|URN syntax diagram{{snd}} namestring]]

* The leading scheme ({{code|urn:}})  is case-insensitive.
* {{code|<NID>}} is the namespace identifier, and may include letters, digits, and <code>-</code>.
* The NID is followed by the namespace-specific string {{code|<NSS>}}, the interpretation of which depends on the specified namespace. The NSS may contain ASCII letters and digits, and many punctuation and special characters. Disallowed ASCII and [[Unicode]] characters may be included if [[percent-encoded]].

In 2017, the syntax for URNs was updated:{{sfnp|RFC 8141|2017}}

* The slash character (<code>/</code>) is now allowed in the NSS to represent names containing slashes from non-URN identifier systems.
* The q-component was added to enable passing of parameters to named resources.
* The r-component was added to enable passing of parameters to resolvers. However, the updated specification notes that it should not be used until its semantics are defined via further standardization.