transclude

Transclude is the inclusion of content from one document within another by reference, rather than by copying. The approach allows the final document to display content that is stored separately, so updates to the source are reflected automatically in all documents that transclude it.

Origin and concept: The term was popularized by Ted Nelson in the Xanadu project of the 1980s to describe a hypertext model in which every fragment of content has a unique, addressable location and can be embedded elsewhere, while maintaining attribution and versioning. Transclusion differs from mere embedding or copying because the included material remains stored in its original location and can be updated independently.

In practice: Transclusion is widely used in wiki systems and other hypertext environments. In wikis, templates or modules can be transcluded into pages, so changes to the template automatically affect all pages that use it. Other forms include including sections of a separate document via XInclude, or embedding external content through iframes. Open transclusion allows the included content to be edited at its source; if the source changes, all transclusions reflect the change. Some systems support parametric transclusion, where parameters supplied to a transcluded fragment customize its output.

Challenges: Transclusion creates dependencies among documents, which can complicate version tracking and caching. Circular references, performance overhead, licensing, attribution, and access control are common concerns.

See also: XInclude, templates, and dynamic content inclusion.