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.
The PHP Life Cycle
Variables from the Inside Out
Setting Up a Build Environment
Your First Extension
Working with Arrays and HashTables
The Resource Data Type
Startup, Shutdown, and a Few Points in Between
Diverting the Stream
Configuration and Linking
Setting Up a Host Environment
Appendix A. A Zend API Reference
Appendix B. PHPAPI
Appendix C. Extending and Embedding Cookbook
Appendix D. Additional Resources