Allows you to modify the value of a field before it’s rendered on the single book template. Here’s an example from one of Novelist’s functions for adding Schema.org markup around the book title:

/**
 * Title: Add Schema
 *
 * Adds schema.org markup around the book title.
 *
 * @param string        $value          Final formatted value
 * @param string        $key            The key that is being filtered
 * @param array         $all_fields     All available book fields
 * @param array         $enabled_fields Only the fields that are enabled
 * @param Novelist_Book $book           Book object
 *
 * @since 1.0.0
 * @return string
 */
function novelist_add_schema_title( $value, $key, $all_fields, $enabled_fields, $book ) {
	if ( empty( $value ) ) {
		return $value;
	}

	return '<span itemprop="name">' . $value . '</span>';
}

add_filter( 'novelist/book/pre-render/title', 'novelist_add_schema_title', 10, 5 );

This filter is run before the value is inserted into the template and before any line breaks are added to the end. If you want to modify a field after those occur, look at the novelist/book/render/$k