The year of copyright.
Since the <copyright-statement> element is intended for display, this element’s contents may not be displayed (but will be available for searching). The <copyright-year> element need not be used, if having the year as part of the <copyright-statement> is sufficient. (See <copyright-statement>.)
<!ELEMENT copyright-year (#PCDATA) >
Text, numbers, or special characters
...
<book-meta>
<book-id>...</book-id>
<book-title-group>
<book-title><italic>C. ELEGANS</italic> II</book-title>
</book-title-group>
...
<publisher>
<publisher-name>Cold Spring Harbor Laboratory Press</publisher-name>
<publisher-loc>Plainview, NY</publisher-loc>
</publisher>
<permissions>
<copyright-statement>© 1997 Cold Spring Harbor Laboratory
Press</copyright-statement>
<copyright-year>1997</copyright-year>
<copyright-holder>Cold Spring Harbor Laboratory Press</copyright-holder>
</permissions>
<abstract>...</abstract>
</book-meta>
...