This tells reading systems (like ADE) what position the XHTML cover should have in the document (must be first to trigger cover behavior), but asks that it not be displayed to the reader as part of the «linear reading order of the publication.» (safaribooksonline.com)
In an installation at the Los Angeles Contemporary Archive, I filled the large wall space with the 1,400 photocopied black and white covers in chronological order of publication from 1971 through 2015, and selected one cover each for year, replacing these with pencil drawings of the covers, thereby inserting my own personal history. (remahortmannfoundation.org)
I think there are probably three key early thinkers (in order of publication) that are most significant: (christianitytoday.com)