Additional Authors

By default the plugin only stores them; the output is up to the theme, through do_action( 'additional_authors_the_authors' ). Since 1.4.0 it can also extend the byline a standard theme already renders: add_filter( 'additional_authors_auto_byline', '__return_true' ); That covers the core/post-author and core/post-author-name blocks used by block themes such as Twenty Twenty-Four and Twenty Twenty-Five, and the the_author() and the_author_posts_link() template tags used by classic themes. It is off by default, because a plugin update should not change what your site outputs. Two things worth knowing:

• Some classic themes — Twenty Twenty-One among them — wrap get_the_author() in a link they build themselves. The additional names then sit inside that link, which points at the main author. If per-author links matter to you, output them yourself with do_action( 'additional_authors_the_authors_posts_links' ) instead.
• The core/post-author block is left untouched when its "Show bio" option is on: a biography belongs to one person, and listing several names above it would read as if it described all of them.

additional_authors_byline_separator sets the separator (default ,), and additional_authors_byline_suffix lets you build the whole appended string, for example to get "Anna, Mark und David": add_filter( 'additional_authors_byline_suffix', function ( $suffix, $ids ) { $names = array_map( fn( $id ) => get_the_author_meta( 'display_name', $id ), $ids ); $last = array_pop( $names ); return ( $names ? ', ' . implode( ', ', $names ) : '' ) . ' und ' . $last; }, 10, 2 );