var citygmlBoundaries = require("citygml-boundaries");
var citygmlValidateRing = require("citygml-validate-ring");
 
var xml = "..."; // Some CityGML
var boundaries = citygmlBoundaries(xml);
 
// Validate exterior ring
citygmlValidateRing(boundaries.exterior[0], function(err, results) {
  if (err) {
    console.log("Exterior ring not valid:", err, results);
  } else {
    console.log("Exterior ring valid");
  }
});