The biblioentry or bibliomixed element to generate a label for.
This template outputs a label to be placed inline at the beginning of a bibliography entry. Labels are created for both biblioentry and bibliomixed elements. The label is typically an abbreviation of the authors' names and the year of publication. In DocBook, it is usually provided with a leading abbrev element. Without a leading abbrev element, this template will instead use the xreflabel or id attribute.