The opening chapters contain high-level conceptual material followed by a brief tour of the tasks you perform when using the feature. Samples are provided next to guide you from simpler to more complex tasks. Finally, reference information provides some of the lower-level details of the various framework components.
In addition to this book, be sure to check for feature updates on the web at http://www.software.ibm.com/ad/smalltalk. Code for the samples will be available for download from the site. Use the keywords, ObjectExtender, or samples from the home page to search for any updates.