The term external semantics describes a variety of technques that can be used to apply semantcis to documents or obejcst that do not natively have them. Some documents have some level of semantics explicitly built into them, for example, schema.org markup can be used in a web page. When there is no explicit semntcis, it may be possible to apply semantics either manually, by describing regions, or automatically using techniques such as data detectors.
Defined on page 405
Used on pages 391, 405