Within a citation to a non-journal item (for example, a book possibly spanning multiple volumes), the <series> element can contain the unique title of the entire series, as shown in the tagged example below.
The word “series” is used in journal publishing with two very different meanings. The element <series> is used for only one of those meanings, and the two elements <series-text> and <series-title> are used only for the other.
Any combination of:
<article> <front>...</front> <body>... </body> <back> ... <ref-list> <ref id="B1"><label>1</label> <citation citation-type="book"> <name><surname>...</surname></name> and <name><surname>...</surname></name> <year>1989</year>. <series>The Birds of South America</series>. <volume>1</volume>. <source>The Oscine Passerines</source>. <publisher-name>University of Texas Press</publisher-name> , <publisher-loc>Austin</publisher-loc> </citation> </ref>...</ref-list>...</back></article>