The <data-about> element identifies the subject
of a property when the subject isn't associated with the context in which
the property is specified. The property itself is expressed by the <data>
element. The <data-about> element handles exception
cases where a property must be expressed somewhere other than inside the actual
subject of the property. The <data-about> element is
particularly useful as a basis for specialization in combination with the <data>
element.
Don't use the <data-about>
element to identify the object of a property. The href attribute
of the <data> element serves that purpose.