docs: function blockDelta(blot, filter = true) {
    return blot
      .descendants(LeafBlot)
      .reduce((delta, leaf) => {
        if (leaf.length() === 0) {
          return delta;
        }
        return delta.insert(leaf.value(), bubbleFormats(leaf, {}, filter));
      }, new Delta())
      .insert('\n', bubbleFormats(blot));
  }