Endnotes with Links
The endnotes for each chapter, which include all the links in the convenient Clickable™ format. You could open them on your phone or other screen device while reading the book.
Some pictures that didn’t make it into the book are also here.
The links in the Kindle version appear to work correctly on devices that play nicely with the Internet (e.g., the Kindle Fire; other pads running the Kindle app).