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xlink:href Href (Linking Mechanism)

An XLink-conformant href; usually an absolute URI identifying the target page of a link.
OPTIONAL on element: <link>
Value Meaning Behavior
Text, numbers, or special characters A pointer (which may be a URL) to a resource Can be used to make this element a live link to a related site
Restriction This attribute may be specified if the element is used.
Tagged Sample

Link to a W3C specification

...
<bibliomixed xml:id="xml2008" xreflabel="XML 1.0 Recommendation">Bray, 
  Tim, Jean Paoli, C. M. Sperberg-McQueen, Eve Maler, François Yergeau. 
  eds. <emphasis role="ital">Extensible Markup Language (XML) 1.0 
  (Fifth Edition)</emphasis>. W3C Recommendation 26 November 2008. 
  <link xlink:href="http://www.w3.org/TR/REC-xml/">http://www.w3.org/TR/REC-xml/</link>.
</bibliomixed>
...