code: function (e) {
  
  		var patternName;
  		var state = e.state;
  
  		if (state === null) {
  			this.skipBack = false;
  			return;
  		} else if (state !== null) {
  			patternName = state.pattern;
  		}
  
  		var iFramePath = "";
  		iFramePath = this.getFileName(patternName);
  		if (iFramePath === "") {
  			iFramePath = "styleguide/html/styleguide.html";
  		}
  
  		var obj = JSON.stringify({
  			"event": "patternLab.updatePath",
  			"path": iFramePath
  		});
  		document.querySelector('.pl-js-iframe').contentWindow.postMessage(obj, urlHandler.targetOrigin);
  		document.getElementById("title").innerHTML = "Pattern Lab - " + patternName;
  		document.querySelector('.pl-js-open-new-window').setAttribute("href", urlHandler.getFileName(patternName));
  	}
docs: based on a click forward or backward modify the url and iframe source
  @param  {Object}      event info like state and properties set in pushState()