readRegionFromDocument(doc) {
    const regions = [];
    for (let n = /** @type {Node} */ (doc.firstChild); n; n = n.nextSibling) {
      if (n.nodeType == Node.ELEMENT_NODE) {
        extend(regions, this.readRegionFromNode(/** @type {Element} */ (n)));
      }
    }
    return regions;
  }
@param {Document} doc Document.
@return {Array<Object>} Region.