%pub-date.class; Publication Date Class Elements

Holds the element <pub-date> and a <pub-date-not-available> element. The later is used as an alternative to <pub-date>; it is an empty element flag meaning “we do not know the publication date”, which does not mean “unpublished”, necessarily, just unknown.
Declaration
<!ENTITY % pub-date.class
                        "pub-date"                                   >