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I'm having trouble working out from
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means that anyURI can be an empty string, can someone elucidate?
[Definition:] anyURI represents a Uniform Resource Identifier Reference
(URI). An anyURI value can be absolute or relative, and may have an optional
fragment identifier (i.e., it may be a URI Reference). This type should be
used to specify the intention that the value fulfills the role of a URI as
defined by [RFC 2396], as amended by [RFC 2732].
The mapping from anyURI values to URIs is as defined in Section 5.4 Locator
Attribute of [XML Linking Language] (see also Section 8 Character Encoding
in URI References of [Character Model]). This means that a wide range of
internationalized resource identifiers can be specified when an anyURI is
called for, and still be understood as URIs per [RFC 2396], as amended by
[RFC 2732], where appropriate to identify resources.
NOTE: Each URI scheme imposes specialized syntax rules for URIs in that
scheme, including restrictions on the syntax of allowed fragement
identifiers. Because it is impractical for processors to check that a value
is a context-appropriate URI reference, this specification follows the lead
of [RFC 2396] (as amended by [RFC 2732]) in this matter: such rules and
restrictions are not part of type validity and are not checked by ·minimally
conforming· processors. Thus in practice the above definition imposes only
very modest obligations on ·minimally conforming· processors.
18.104.22.168 Lexical representation
The ·lexical space· of anyURI is finite-length character sequences which,
when the algorithm defined in Section 5.4 of [XML Linking Language] is
applied to them, result in strings which are legal URIs according to [RFC
2396], as amended by [RFC 2732].
NOTE: Spaces are, in principle, allowed in the ·lexical space· of anyURI,
however, their use is highly discouraged (unless they are encoded by %20).
22.214.171.124 Constraining facets
anyURI has the following ·constraining facets·: