drawSpacerElem(elem, rowHeight, isRtl) {
    if (!DebugDrawer.config.elemSpacers) {
      return;
    }

    const width = Math.abs(elem.width);
    const isNegativeSpacing = elem.width < 0;
    let xPos = isNegativeSpacing ? elem.xPos - width : elem.xPos;
    if (isRtl) {
      xPos = -(xPos + width);
    }
    const yPos = elem.centerline - elem.height / 2;
    this.debugElements_.push(
      Blockly.utils.dom.createSvgElement(
        'rect',
        {
          'class': 'elemSpacerRect blockRenderDebug',
          'x': xPos,
          'y': yPos,
          'width': width,
          'height': elem.height,
          'stroke': 'pink',
          'fill': isNegativeSpacing ? 'black' : 'pink',
          'fill-opacity': '0.5',
          'stroke-width': '1px',
        },
        this.svgRoot_,
      ),
    );
  }
Draw a debug rectangle for a horizontal spacer.
@param {!Blockly.blockRendering.InRowSpacer} elem The spacer to render.
@param {number} rowHeight The height of the container row.
@param {boolean} isRtl Whether the block is rendered RTL.
@protected