Database handle for the object. It is of XML type ID, so is constrained to be
unique in the XML document within which it occurs. An external identifier for the object in
the form of a URI may be constructed using standard XML and XPointer methods. This is done
by concatenating the URI for the document, a fragment separator, and the value of the id
attribute.

The 'actuate' attribute is used to communicate the desired timing 
of traversal from the starting resource to the ending resource; 
it's value should be treated as follows:
onLoad - traverse to the ending resource immediately on loading 
         the starting resource 
onRequest - traverse from the starting resource to the ending 
            resource only on a post-loading event triggered for 
            this purpose 
other - behavior is unconstrained; examine other markup in link 
        for hints 
none - behavior is unconstrained

The 'show' attribute is used to communicate the desired presentation 
of the ending resource on traversal from the starting resource; it's 
value should be treated as follows: 
new - load ending resource in a new window, frame, pane, or other 
      presentation context
replace - load the resource in the same window, frame, pane, or 
          other presentation context
embed - load ending resource in place of the presentation of the 
        starting resource
other - behavior is unconstrained; examine other markup in the 
        link for hints 
none - behavior is unconstrained

<div>
  <h3>lang (as an attribute name)</h3>
  <p>denotes an attribute whose value is a language code for the natural language of the content of any element; its value is inherited. This name is reserved by virtue of its definition in the XML specification.</p>
</div>
<div>
  <h4>Notes</h4>
  <p>Attempting to install the relevant ISO 2- and 3-letter codes as the enumerated possible values is probably never going to be a realistic possibility.</p>
  <p>See BCP 47 at
    <a href="http://www.rfc-editor.org/rfc/bcp/bcp47.txt">http://www.rfc-editor.org/rfc/bcp/bcp47.txt</a>and the IANA language subtag registry at
    <a href="http://www.iana.org/assignments/language-subtag-registry">http://www.iana.org/assignments/language-subtag-registry</a>for further information.</p>
  <p>The union allows for the 'un-declaration' of xml:lang with the empty string.</p>
</div>