The DITA design has a unified content reuse mechanism by which an element can replace itself with the content of a like element elsewhere, either in the current topic or in a separate topic that shares the same content models. The distinction between reusable content and reusing content, often a problem for authors trying to use file and text entities, disappears: Any element with an ID, in any DITA topic, is reusable by conref.

DITA's conref "transclusion" mechanism is similar to the SGML conref mechanism, which uses an empty element as a reference to a complete element elsewhere. However, DITA requires that at least a minimal content model for the referencing element be present, and performs checks during processing to ensure that the replacement element is valid in its new context. This mechanism goes beyond standard XInclude, in that content can be incorporated only when it is equivalent: If there is a mismatch between the reusing and reused element types, the conref is not resolved. It also goes beyond standard entity reuse, in that it allows the reused content to be in a valid XML file with a DTD. The net result is that reused content gets validated at authoring time, rather than at reuse time, catching problems at their source.

Content referencing can be used at any scope of elements in a DITA document, from a keyword phrase that contains only PCDATA to a whole topic with other nested topics. Conref can cross file boundaries, using the same syntax as that of the href attribute on the xref element. If your authoring DTD allows topic nesting, you can create a set of minimal child topics and then use their conref attributes to pull in content from fully populated topics in other files.