To divide a document's chapters into logical groupings, you can use the part element to provide a title and optional introduction to group the chapter under. The part element will typically be used with larger books that contain different types or categories of information. Do not use just to get another level of hierarchy in a standard book. A good example would be a large, complicated install guide or upgrade guide that contains different deployment or upgrade scenarios. In this case, you can use the part element to create main headings for each scenario and then group the relevant chapters under the headings.