Chapters & markers

Chapters serve two purposes: as navigable list rows and, optionally, as markers drawn on the waveform.

showChapterMarkers controls the waveform markers, and its null default is a smart heuristic:

null resolves to true only when there is exactly one track that has chapters. So a single chaptered episode shows its chapters as waveform markers automatically; multi-track playlists instead show chapters as expandable list sub-lists.
Set showChapterMarkers explicitly (true/false, or data-show-chapter-markers) to override the heuristic.

Chapters are converted to markers only when the track has no explicit data-markers (markers.length === 0). Explicit data-markers always win, and each chapter-derived marker uses data-color if present, otherwise chapterMarkerColor.

While a track plays, the active chapter row is re-highlighted on every onTimeUpdate — the row gets the .wp-active class and aria-current="true".