In reply to Justin Tadlock.

Looking things over, it's sort of an "unofficial" argument, in that it's not listed at https://developer.wordpress.org/reference/functions/wp_list_bookmarks/ as an available/default, but you can pass it in as one of the args indexes, and it'll make it all the way through to _walk_bookmarks() where it is one of the defaults which is boolean true when an image is saved :D

The more I know.