A lot of the material in the
https://ampl.com/NEW/ . . . pages was included in the 2nd edition of the AMPL book. Some of that material is indeed newer than the book, however. We have covered the newer material in the RESOURCES / NEW FEATURES menu of the current AMPL website, along with additions to the AMPL system (like the APIs) that supplement the modeling language. Thus between the book and those menu items, readers should have what they need to know about current AMPL features.
We are developing new reference material that will be helpful to AMPL users, such as a guide to all AMPL option settings. This material will be published on our website as a supplement to the book.