Model

<!ENTITY % event-model  "(event-desc?, article-id*, 
                          (%article-version.class;)?,
                          ( (%pub-date.class;)* | 
                             pub-date-not-available?),
                          (%date.class;)*,
                          issn*, issn-l?, isbn*, permissions?,
                          notes*, self-uri*)"                        >

Expanded Model

(event-desc?, article-id*, (article-version | article-version-alternatives)?, ( (pub-date)* | pub-date-not-available?), (date)*, issn*, issn-l?, isbn*, permissions?, notes*, self-uri*)