code: function FeatureCollection(featureCollection) {
          crs(featureCollection);
          bbox(featureCollection);
          if (featureCollection.properties !== undefined) {
              errors.push({
                  message: 'FeatureCollection object cannot contain a "properties" member',
                  line: featureCollection.__line__
              });
          }
          if (featureCollection.coordinates !== undefined) {
              errors.push({
                  message: 'FeatureCollection object cannot contain a "coordinates" member',
                  line: featureCollection.__line__
              });
          }
          if (!requiredProperty(featureCollection, 'features', 'array')) {
              if (!everyIs(featureCollection.features, 'object')) {
                  return errors.push({
                      message: 'Every feature must be an object',
                      line: featureCollection.__line__
                  });
              }
              featureCollection.features.forEach(Feature);
          }
      }
docs: https://tools.ietf.org/html/rfc7946#section-3.3