Specifies that this property attribute takes a Uniform Resource Name.
<URN/>
None.
Parent: attribute.
Children: None.
A URN identifies a resource in a persistent, location-independent way. URNs are a subset of URIs.
This element is one of several you can use to specify the type of a property attribute's value. The complete list includes boolean, class-name, class-names, date, decimal, enumeration, file-path, integer, QNAME, text, URI, URL, URN, XML, or custom. Note that you may use only one of these types for a given attribute.