Since language has a tendency to change over time and certain references lose their currency, reprints of classic works of literature sometimes have an endnotes or footnotes section, explaining some of the references. These usually explain: * Customs, technological devices and societal statuses of the time period that are no longer recognized. * Word uses which have since shifted, and wordplay about such. * Connections with the author's life period, and random guesswork at what inspired passages * Allusions or in-references that were commonly recognized, but are now more obscure.