"Transclusion" is a term introduced by Ted Nelson to define virtual inclusion, the process of including something by reference rather than by copying. This is fundamental to the Xanadu designs; originally transclusions were implemented using hyperlinks, but it was later discovered that in fact hyperlinks could be implemented using transclusions! Transclusions permit storage efficiency for multiple reasonably similar documents, such as those generated by versions and alternates as discussed above [pam_where].