Introduction
One essential part of Ted Nelson's original concept of Xanadu was that links between documents be bi-directional--when a link was made to a document, the linked-to text would become a link back to the document that referenced it. This was believed to be an essential component of an open hypertext system intended for discussion of complex issues, and a great improvement over current forms of scholarly publication.
With the advent of the World-Wide Web, links have come into the mainstream of writing and publishing, but these links are unidirectional--there's no way to know if a link has been made to your document, and no way to attach comments of your own to documents you read on the Web. In the Web, as it exists today, we have forward links but no back links.
Hack Links is a crude mechanism that provides a limited back link capability for Web documents. Despite its many shortcomings, it may prove useful to demonstrate the utility of back links and obtain practical experience in their use which can guide the evolution of a more practical and comprehensive facility for eventual inclusion in the HTML standard with Web client and server support.