You may want to add a byline as a separate article element.
The reason you may want to do this is to avoid that the top byline (typically the first paragraph of the body text) appears as first content also on the Web article - you may want to have it on a different position on Web than in print.
In such case, add a new article element to the schema, or use an existing one, e.g. intro, if your articles do not need an intro element.
See also