In external-data-entity rules, the attributes of the entity that triggered the rule are referred to using the attribute herald.
Entities named in ENTITY and ENTITIES attributes may also have data attributes. You can use the data-attribute operator to access these data attributes.
The keyword data-attribute can be used in the same way that attribute is used elsewhere. The data attribute name must always be followed by of and, in parentheses, the identification of the attribute value or item containing the entity name.