zval* Array API
Summary
You've just spent a long chapter learning about one of the most prevalent structures in the Zend Engine and PHP Coresecond only to the zval* of course. You compared different data storage mechanisms and were introduced to a large swath of the API that you'll use repeatedly.
By now you should have enough tools amassed to implement a fair portion of the standard extension. In the next few chapters you'll round off the remaining zval data types by exploring resources and objects.