docs: function Indicator (data) {
      this.direction = 'row' // 'column' is not temporarily supported.
      this.amount = data.extra.amount
      this.index = data.extra.index
      this.sliderWidth = data.extra.width
      this.sliderHeight = data.extra.height
      const styles = data.style || {}
      this.data = data
      this.style.width.call(this, styles.width)
      this.style.height.call(this, styles.height)
      this.itemColor = styles.itemColor || DEFAULT_ITEM_COLOR
      this.itemSelectedColor = styles.itemSelectedColor
        || DEFAULT_ITEM_SELECTED_COLOR
      this.items = []
      Atomic.call(this, data)
    }