Integer offset = 0;
while (chapterMatcher.find(offset)) {
String title = chapterMatcher.group(1).trim();
String label = chapterMatcher.group(2) == null ? new TitleSlug(title).toString() : chapterMatcher.group(2);
String content = chapterMatcher.group(3);
offset = chapterMatcher.end(3);
String introduction = extractIntroduction(content);