Permanence and consistency of scientific records seem to demand immutability. But perhaps a relaxed variant that allows extensions, but not alterations, would be useful. Extensibility Paper publications link with the body of knowledge in which they reside through outgoing references and incoming citations. Once published, references and the publications to which they refer are immutable. This represents a strength and a weakness of paper publication.
Hyperlinks are both more convenient and more flexible than textual references.
A price is paid in the lack of referential integrity the Web does not update references when the target moves. Not all resources referenced in an electronic publication are necessarily immutable. This opens the possibility of later extensions to publications. We can exploit this difference, for example to structure publications with alternative reading paths. Referential integrity should be at least as good as it is for paper publications.