Element: ISSN International Standard Serial Number
... <ref> <mixed-citation> <person-group person-group-type="author"> <string-name><surname>Forster</surname> <given-names>Anne Williams</given-names></string-name>, <string-name><surname>Young</surname> <given-names>John G.</given-names></string-name> </person-group> <article-title>Systematic review of day hospital care for elderly people</article-title>. <source>British Medical Journal</source>. <day>27</day> <month>03</month> <year iso-8601-date="1999">1999</year>; <volume>318</volume>(<issue>7187</issue>): <fpage>837</fpage>&ndash;<lpage>841</lpage>. ISSN: <issn>0959-8138</issn>. <pub-id>10092260</pub-id>. </mixed-citation> </ref> ...

... <ref> <element-citation> <person-group person-group-type="author"> <name><surname>Forster</surname> <given-names>Anne Williams</given-names></name> <name><surname>Young</surname> <given-names>John G.</given-names></name> </person-group> <article-title>Systematic review of day hospital care for elderly people</article-title> <source>British Medical Journal</source> <volume>318</volume> <issue>7187</issue> <fpage>837</fpage> <lpage>841</lpage> <day>27</day> <month>03</month> <year iso-8601-date="1999">1999</year> <issn>0959-8138</issn> <pub-id>10092260</pub-id> </element-citation> </ref> ...