What Regions Are Available and What is the Basic HTML Structure?

In order of output in the source code, the following regions are available:

1. Header
2. Preface First
3. Preface Middle
4. Preface Last
5. Primary Pre-Title
6. Primary Post-Title
7. Primary (main content area)
8. Secondary First
9. Secondary Middle
10. Secondary Last
11. Tertiary First
12. Tertiary Middle
13. Tertiary Last
14. Postscript First
15. Postscript Middle
16. Postscript Last
17. Footer
18. Closure

While that may seem like a lot of regions, keep in mind that the overall structure is pretty simple and clean (see image below).