message: stringify value when it is an object or array
diff: public getOpeningTag(selfClose: boolean) {
  var attrs = '';
  - function outputAttr(attrName, attrValue) {
  + function outputAttr(attrName: string, attrValue: any) {
  if (attrValue == null || typeof attrValue === 'undefined') return;
  + if (Array.isArray(attrValue) || typeof attrValue === 'object') {
  + attrValue = JSON.stringify(attrValue);
  + }
  +
  if (typeof attrValue === 'string') {
  attrValue = XmlTag.escapeString(attrValue);
  }
  