readFlatCurveRing(node, objectStack) {
    /** @type {Array<LineString>} */
    const lineStrings = pushParseAndPop(
      [],
      this.MULTICURVE_PARSERS,
      node,
      objectStack,
      this,
    );
    const flatCoordinates = [];
    for (let i = 0, ii = lineStrings.length; i < ii; ++i) {
      extend(flatCoordinates, lineStrings[i].getFlatCoordinates());
    }
    return flatCoordinates;
  }
@param {Element} node Node.
@param {Array<*>} objectStack Object stack.
@return {Array<number>|undefined} Polygon.