+ /**
+ * Get the main info to display for this book (a title, an author, a
+ * source/type name...).
+ * <p>
+ * Note that when {@link MetaData} about the book are present, the title
+ * inside is returned instead of the actual value (that way, we can update
+ * the {@link MetaData} and see the changes here).
+ *
+ * @return the main info, usually the title
+ */