This is a new maintenance release for the old 1.2 series. The new ECMAScript 6 specification has a proposal for String.prototype.contains that unfortunately conflicts with the MooTools implementation of contains.
Firefox 18 already ships this new version of contains. This is not a problem for MooTools 1.3.x and onward, but this breaks MooTools 1.2.5, especially the code inside the MooTools framework that utilized this method, like selectors.
This new 1.2.6 release solves these issues by overwriting the native version with the MooTools version of String.prototype.contains.
For the next MooTools version, 1.5, we will use the standard ES6 version. If you rely on the old behavior (which is only when you use the second argument), it will be possible to use the old version through the compatibility layer.
Until recently, French literature about MooTools was pretty much non-existent. Thanks to Xavier Lecomte, now there is a very good book about MooTools in your native tongue that will get you up to speed in no time.
Découvrez Mootools - Un framework JavaScript pour des sites dynamiques et interactifs (Discover MooTools - A javascript framework for dynamic and interactive websites) is aimed at beginner and intermediate developers who wish to create spectacular effects using MooTools. This book does not go deep into topics that would likely only confuse you, but instead it keeps everything simple and provides many clear cut examples and illustrations that will facilitate your understanding. Priced at 12.5 Euros (~15$) it’s a must-have if you’re looking to learn MooTools.
As the author says, it does not cover the entire framework. Instead, Xavier Lecomte selected the most commonly used MooTools pieces and explains them in detail. Throughout this book, you’ll learn how to create classes, handle DOM elements, create AJAX requests and create effects using Fx classes. The latter is probably the most discussed topic of this book as it goes through almost every Fx-based class in MooTools. When it comes to Fx classes, the most complex part is probably options. Although they are well named, they could be difficult to grasp, especially to the novice user. This book makes this type of functionality very clear by explaining all the options for each class discussed, at times, through the use of illustrations. The Fx chapter wraps up with a complete example, where the author builds a pong game using tools explained throughout the chapter.
Finally, the book discusses work done by the MooTools community. Although it does not go deeply into each project (most of them would require a book on their own), it gives a good idea of what MooTools is able to offer.
To conclude, if you're a native French speaker interested in learning MooTools, this book is a must-have, especially at that price. I hope Xavier Lecomte will continue writing about MooTools, the in-depth detailing of this book is amazing and will certainly benefit many.