The form of each book may be identical or allow for variations in methodology among the many authors who collaborate to write a full commentary. Each book's commentary generally consists of a background and introductory section, followed by detailed commentary of the book pericope-by-pericope or verse-by-verse. Before the 20th century, a commentary would be written by a sole author, but in the recent period, a publishing board will commission a team of scholars to write a commentary, with each volume being divided out among them.