docs: function removeClearedSpans(spans) {
    if (!spans) return null
    let out
    for (let i = 0; i < spans.length; ++i) {
      if (spans[i].marker.explicitlyCleared) { if (!out) out = spans.slice(0, i) }
      else if (out) out.push(spans[i])
    }
    return !out ? spans : out.length ? out : null
  }