code: function(id, xnew, xold) {
  		edbml.Update.prototype.setup.call(this);
  		this.id = id;
  		this._xnew = xnew;
  		this._xold = xold;
  		return this;
  	}
docs: Setup update.
  @param {String} id
  @param {Element} xnew
  @param {Element} xold
  @returns {edbml.AttsUpdate}