How to use the moddle.Moddle.prototype function in moddle

/**
 * A sub class of {@link Moddle} with support for import and export of BPMN 2.0 xml files.
 *
 * @class BpmnModdle
 * @extends Moddle
 *
 * @param {Object|Array} packages to use for instantiating the model
 * @param {Object} [options] additional options to pass over
 */
export default function BpmnModdle(packages, options) {
  Moddle.call(this, packages, options);
}

BpmnModdle.prototype = Object.create(Moddle.prototype);


/**
 * Instantiates a BPMN model tree from a given xml string.
 *
 * @param {String}   xmlStr
 * @param {String}   [typeName='bpmn:Definitions'] name of the root element
 * @param {Object}   [options]  options to pass to the underlying reader
 * @param {Function} done       callback that is invoked with (err, result, parseContext)
 *                              once the import completes
 */
BpmnModdle.prototype.fromXML = function(xmlStr, typeName, options, done) {

  if (!isString(typeName)) {
    done = options;
    options = typeName;