code: function Mex(callContext, url) {
    this._log = new Logger('MEX', callContext._logContext);
    this._callContext = callContext;
    this._url = url;
    this._dom = null;
    this._mexDoc = null;
    this._usernamePasswordPolicy = {};
    this._log.verbose('Mex created');
    this._log.verbose('Mex created with url: ' + url, true);
  }
docs: Create a new Mex object.
  @private
  @constructor
  @param {object} callContext Contains any context information that applies to the request.
  @param {string} url  The url of the mex endpoint.