Section 14.9: Error Hooks Up Chapter 14: Extensions Section 14.11: New Types 

14.10 Map Files

These will for the first time enable you to have full overview of what your code is doing, how, and where. Indispensable for debugging and understanding unfamiliar code, and the behaviour of the compiler.
 Section 14.9: Error Hooks Up Chapter 14: Extensions Section 14.11: New Types