Model for the <issue-part> element.
A publisher may split an issue into two or more separately bound or separately issued parts. This element holds the identifiers (titles, part numbers, etc.) for those publishing components.
Design Note: All inline mixes begin with an OR bar; since %just-rendition; is an inline mix, the OR bar is already there, or %just-rendition; is itself a null string, and the OR bar need not be added to %issue-part-elements;.
<!ENTITY % issue-part-elements "%just-rendition;" >