Right now, only text can function as links. This is constraining. One should be able to make any selection a link to any other selection.

Transclusion allows bits of other parts of documents to not only be linked to, but included within the content of another document or within the same document. A selection is a generalization of a quotation, but instead of making a copy, we have something analogous to an iframe. The same source selection can occur in more than one location, with a link to the original. Electronic notebooks can do this, because they do not suffer from the limitations of the paper medium.