Reference to an XML Schema fragment that specifies the content model of the propertys value. This is in conformance with the XML Schema Section 4.14 Referencing Schemas from Elsewhere.

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

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.