Best Practice 4.23.8.1. Understand the Role of a Preface.
Chicago Manual of Style [1, 1.49] begins with “Material normally contained in an author’s preface includes reasons for undertaking the work, method of research, …” Note that a preface is not introductory content and is not an introduction. It is written from the author’s point-of-view, and may include information about why they are qualified to write on the topic of the book. If there are several editions, the prefaces to the newer editions are placed first. See the related Best Practice 26.3.0.1.