Typically, the year of publication for a book or other work, but also the year “historical” events in a publishing cycle occurred, for example, the year a manuscript was last updated.
The <year> element is used in two contexts: as a part of the metadata concerning book or book component (such as a chapter), and as part of a description of a cited work inside a bibliographic reference (<citation>) element.
Conversion Note: When possible, the year should be expressed as a 4-digit number, for example, “1776”, “1924”, or “0042”.
<!ELEMENT year (#PCDATA) >
Text, numbers, or special characters
...<ref-list> <title>References</title> <ref id="bid.41"> <label>1</label> <citation> <person-group> <name><surname>Olson</surname><given-names>M</given-names></name> ... </person-group> <article-title>A common language for physical mapping of the human genome</article-title> <source>Science</source> <year>1989</year> <volume>245</volume> <issue>4925</issue> <fpage>1434</fpage> <lpage>1435</lpage> <pub-id pub-id-type="pmid">2781285</pub-id> </citation> </ref> </ref-list>...