# Chapters & markers

> Chapter navigation and waveform markers.

## 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"`.