function parseNode(parsersNS, node, objectStack, thisArg) {
  let n;
  for (n = node.firstElementChild; n; n = n.nextElementSibling) {
    const parsers = parsersNS[n.namespaceURI];
    if (parsers !== undefined) {
      const parser = parsers[n.localName];
      if (parser !== undefined) {
        parser.call(thisArg, n, objectStack);
      }
    }
  }
}
Parse a node using the parsers and object stack.
@param {Object<string, Object<string, Parser>>} parsersNS
    Parsers by namespace.
@param {Element} node Node.
@param {Array<*>} objectStack Object stack.
@param {*} [thisArg] The object to use as `this`.