render(): void {
    super.render()

    if (!this.model.visible) {
      hide(this.el)
      return
    }

    const panel = this.model.panel!

    this.el.style.position = "absolute"
    this.el.style.left = `${panel._left.value}px`
    this.el.style.top = `${panel._top.value}px`
    this.el.style.width = `${panel._width.value}px`
    this.el.style.height = `${panel._height.value}px`

    this.el.style.overflow = "hidden"

    const toolbar = this._toolbar_views[this.model.toolbar.id]
    toolbar.render()

    empty(this.el)
    this.el.appendChild(toolbar.el)
    show(this.el)
  }

  update_position(): void {
    super.update_position()

    this.header_el.style.position = "absolute" // XXX: do it in position()
    position(this.header_el, this.header.bbox)

    const loc = this.model.tabs_location
    const vertical = loc == "above" || loc == "below"

    const scroll_el_size = size(this.scroll_el)
    const headers_el_size = scroll_size(this.headers_el)
    if (vertical) {
      const {width} = this.header.bbox
      if (headers_el_size.width > width)
        this.wrapper_el.style.maxWidth = `${width - scroll_el_size.width}px`
      else
        undisplay(this.scroll_el)
    } else {
      const {height} = this.header.bbox
      if (headers_el_size.height > height)
        this.wrapper_el.style.maxHeight = `${height - scroll_el_size.height}px`
      else
        undisplay(this.scroll_el)
    }

    const {child_views} = this
    for (const child_view of child_views)
      hide(child_view.el)

    show(child_views[this.model.active].el)
  }

  render() {
    super.render();

    if (!this.model.visible) {
      hide(this.el);
      return;
    }

    const { panel } = this.model;

    this.el.style.position = "absolute";
    this.el.style.left = `${panel._left.value}px`;
    this.el.style.top = `${panel._top.value}px`;
    this.el.style.width = `${panel._width.value}px`;
    this.el.style.height = `${panel._height.value}px`;

    this.el.style.overflow = "hidden";

    const toolbar = this._toolbar_views[this.model.toolbar.id];
    toolbar.render();

    empty(this.el);
    this.el.appendChild(toolbar.el);
    return show(this.el);
  }

  update_position(): void {
    super.update_position()

    position(this.header_el, this.header.bbox)

    const {child_views} = this
    for (const child_view of child_views)
      hide(child_view.el)

    show(child_views[this.model.active].el)
  }

  on_active_change(): void {
    const i = this.model.active

    const headers = children(this.header_el)
    for (const el of headers)
      el.classList.remove("bk-active")

    headers[i].classList.add("bk-active")

    const {child_views} = this
    for (const child_view of child_views)
      hide(child_view.el)

    show(child_views[i].el)
  }

  _css_text(ctx: Context2d, text, sx, sy, angle) {
    let line_dash;
    hide(this.el);

    this.visuals.text.set_value(ctx);
    const bbox_dims = this._calculate_bounding_box_dimensions(ctx, text);

    // attempt to support vector string-style ("8 4 8") line dashing for css mode
    const ld = this.visuals.border_line.line_dash.value();
    if (isArray(ld)) {
      if (ld.length < 2) {
        line_dash = "solid";
      } else {
        line_dash = "dashed";
      }
    }
    if (isString(ld)) {
        line_dash = ld;
      }

    this.visuals.border_line.set_value(ctx);
    this.visuals.background_fill.set_value(ctx);

    this.el.style.position = 'absolute';
    this.el.style.left = `${sx + bbox_dims[0]}px`;
    this.el.style.top = `${sy + bbox_dims[1]}px`;
    this.el.style.color = `${this.visuals.text.text_color.value()}`;
    this.el.style.opacity = `${this.visuals.text.text_alpha.value()}`;
    this.el.style.font = `${this.visuals.text.font_value()}`;
    this.el.style.lineHeight = "normal"; // needed to prevent ipynb css override

    if (angle) {
      this.el.style.transform = `rotate(${angle}rad)`;
    }

    if (this.visuals.background_fill.doit) {
      this.el.style.backgroundColor = `${this.visuals.background_fill.color_value()}`;
    }

    if (this.visuals.border_line.doit) {
      this.el.style.borderStyle = `${line_dash}`;
      this.el.style.borderWidth = `${this.visuals.border_line.line_width.value()}px`;
      this.el.style.borderColor = `${this.visuals.border_line.color_value()}`;
    }

    this.el.textContent = text;
    return show(this.el);
  }

  protected _css_box(sleft: number, sright: number, sbottom: number, stop: number): void {
    const sw = Math.abs(sright - sleft)
    const sh = Math.abs(sbottom - stop)

    this.el.style.left = `${sleft}px`
    this.el.style.width = `${sw}px`
    this.el.style.top = `${stop}px`
    this.el.style.height = `${sh}px`
    this.el.style.borderWidth = `${this.model.properties.line_width.value()}px`
    this.el.style.borderColor = this.model.properties.line_color.value()
    this.el.style.backgroundColor = this.model.properties.fill_color.value()
    this.el.style.opacity = this.model.properties.fill_alpha.value()

    // try our best to honor line dashing in some way, if we can
    const ld = this.model.properties.line_dash.value().length < 2 ? "solid" : "dashed"
    this.el.style.borderStyle = ld

    show(this.el)
  }

  protected _css_text(ctx: Context2d, text: string, sx: number, sy: number, angle: number): void {
    hide(this.el)

    this.visuals.text.set_value(ctx)
    const bbox_dims = this._calculate_bounding_box_dimensions(ctx, text)

    // attempt to support vector string-style ("8 4 8") line dashing for css mode
    const ld = this.visuals.border_line.line_dash.value()
    const line_dash = ld.length < 2 ? "solid" : "dashed"

    this.visuals.border_line.set_value(ctx)
    this.visuals.background_fill.set_value(ctx)

    this.el.style.position = 'absolute'
    this.el.style.left = `${sx + bbox_dims[0]}px`
    this.el.style.top = `${sy + bbox_dims[1]}px`
    this.el.style.color = `${this.visuals.text.text_color.value()}`
    this.el.style.opacity = `${this.visuals.text.text_alpha.value()}`
    this.el.style.font = `${this.visuals.text.font_value()}`
    this.el.style.lineHeight = "normal"; // needed to prevent ipynb css override

    if (angle) {
      this.el.style.transform = `rotate(${angle}rad)`
    }

    if (this.visuals.background_fill.doit) {
      this.el.style.backgroundColor = `${this.visuals.background_fill.color_value()}`
    }

    if (this.visuals.border_line.doit) {
      this.el.style.borderStyle = `${line_dash}`
      this.el.style.borderWidth = `${this.visuals.border_line.line_width.value()}px`
      this.el.style.borderColor = `${this.visuals.border_line.color_value()}`
    }

    this.el.textContent = text
    show(this.el)
  }

  _css_box(sleft, sright, sbottom, stop) {
    const sw = Math.abs(sright-sleft);
    const sh = Math.abs(sbottom-stop);

    this.el.style.left = `${sleft}px`;
    this.el.style.width = `${sw}px`;
    this.el.style.top = `${stop}px`;
    this.el.style.height = `${sh}px`;
    this.el.style.borderWidth = `${this.model.line_width.value}px`;
    this.el.style.borderColor = this.model.line_color.value;
    this.el.style.backgroundColor = this.model.fill_color.value;
    this.el.style.opacity = this.model.fill_alpha.value;

    // try our best to honor line dashing in some way, if we can
    let ld = this.model.line_dash;
    if (isArray(ld)) {
      ld = ld.length < 2 ? "solid" : "dashed";
    }
    if (isString(ld)) {
      this.el.style.borderStyle = ld;
    }

    return show(this.el);
  }

  protected _draw_tips(): void {
    const {data} = this.model
    empty(this.el)
    hide(this.el)

    if (this.model.custom)
      this.el.classList.add("bk-tooltip-custom")
    else
      this.el.classList.remove("bk-tooltip-custom")

    if (data.length == 0)
      return

    const {frame} = this.plot_view

    for (const [sx, sy, content] of data) {
      if (this.model.inner_only && !frame.bbox.contains(sx, sy))
          continue

      const tip = div({}, content)
      this.el.appendChild(tip)
    }

    const [sx, sy] = data[data.length - 1] // XXX: this previously depended on {sx, sy} leaking from the for-loop

    const side = compute_side(this.model.attachment, sx, sy, frame._hcenter.value, frame._vcenter.value)

    this.el.classList.remove("bk-right")
    this.el.classList.remove("bk-left")
    this.el.classList.remove("bk-above")
    this.el.classList.remove("bk-below")

    const arrow_size = 10  // XXX: keep in sync with less

    show(this.el)  // XXX: {offset,client}Width() gives 0 when display="none"

    // slightly confusing: side "left" (for example) is relative to point that
    // is being annotated but CS class "bk-left" is relative to the tooltip itself
    let left: number, top: number
    switch (side) {
      case "right":
        this.el.classList.add("bk-left")
        left = sx + (this.el.offsetWidth - this.el.clientWidth) + arrow_size
        top = sy - this.el.offsetHeight/2
        break
      case "left":
        this.el.classList.add("bk-right")
        left = sx - this.el.offsetWidth - arrow_size
        top = sy - this.el.offsetHeight/2
        break
      case "below":
        this.el.classList.add("bk-above")
        top = sy + (this.el.offsetHeight - this.el.clientHeight) + arrow_size
        left = Math.round(sx - this.el.offsetWidth/2)
        break
      case "above":
        this.el.classList.add("bk-below")
        top = sy - this.el.offsetHeight - arrow_size
        left = Math.round(sx - this.el.offsetWidth/2)
        break
      default:
        throw new Error("unreachable code")
    }

    if (this.model.show_arrow)
      this.el.classList.add("bk-tooltip-arrow")

    // TODO (bev) this is not currently bulletproof. If there are
    // two hits, not colocated and one is off the screen, that can
    // be problematic
    if (this.el.childNodes.length > 0) {
      this.el.style.top = `${top}px`
      this.el.style.left = `${left}px`
    } else
      hide(this.el)
  }