docs: function write_props_xlml(wb/*:Workbook*/, opts)/*:string*/ {
  	var o/*:Array<string>*/ = [];
  	/* DocumentProperties */
  	if(wb.Props) o.push(xlml_write_docprops(wb.Props, opts));
  	/* CustomDocumentProperties */
  	if(wb.Custprops) o.push(xlml_write_custprops(wb.Props, wb.Custprops, opts));
  	return o.join("");
  }