> A ToC doesn't actually work like an API.

> A ToC cares what order it's in. You can't move Chapter 4 to before Chapter 2 or the implementation has to change.

This isn't true.

  Table of Contents

  Foreword.................i
  Introduction............ii
  Preface................xvi
  Chapter 1................1
  Chapter 2...............17
  Chapter 3...............30
  Chapter 4...............51
  Chapter 5...............58
  Chapter 6...............76

Compare:

  Table of Contents

  Foreword.................i
  Introduction............ii
  Preface................xvi
  Chapter 4...............51
  Chapter 1................1
  Chapter 2...............17
  Chapter 3...............30
  Chapter 5...............58
  Chapter 6...............76

Note that real-world tables of contents behave in the second way. It's not at all uncommon to see chapters listed in order, followed by other materials (commonly illustrations) which are listed last in the table of contents while being physically interspersed among the chapters.