Template:AuthorMask doc

authormask – This parameter is primarily intended for use in bibliographies where multiple works by a single author are listed. It replaces the name of the first author (which must still be provided to garner metadata) with a strike-thru dash (—) authormask em in length. So if |authormask=1 then the dash will be one em in length, if |authormask=2 it will be two em long and so on. Set authormask to a text value to display a word instead – for example, 'with'. You must still include |last= and |first= for metadata purposes.