[ 2014-05-19 Beman Dawes supplied wording. ]

The design benefited from discussions with Jamie Allsop, who was the source of the original NB comment. Thanks to Bjorn Reese for corrections and suggestions. Although there was also discussion and experimentation with additional relative functions that took into account symlinks and normalization, these are not proposed here since even the proponents of such functions were unsure of appropriate semantics.