One item in a bibliographic list (typically a citation describing a referenced work although some books may place notes, as well as citations, in a bibliographic list)
<!ELEMENT ref %ref-model; >
The following, in order:
...<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>...
references.ent