The @keyref attribute
The @keyref attribute provides an indirect, late-bound reference to topics, to collections of topics (ditabase), to maps, to referenceable portions of maps, to non-DITA documents, to external URIs, or to XML content contained within a key definition topic reference. When the DITA content is processed, the key references are resolved using key definitions from DITA maps.
For elements that only refer to topics or non-DITA resources, the value of the @keyref attribute is a key name. For elements that can refer to elements within maps or topics, the value of the @keyref attribute is a key name, a slash ("/"), and the ID of the target element, where the key name must be bound to either the map or topic that contains the target element.