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 may only refer to topics or non-DITA resources, the value of the keyref attribute is a key name. For elements that may refer to elements within maps or topics, the value of the keyref attribute is a key name, a solidus ("/"), 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.