How do I edit the Preface, Introduction, Epilogue and other extra sections? (from v1.6.3)
On the book's page, hover a section name in the "Include in book" list and click the pencil icon. A Markdown editor opens; your text is saved exactly as written and the
section keeps its correct place in the book. Do NOT edit files by hand or re-import the manuscript to change these sections — the editor is the supported way.