Increase zoom level in WebView

webViewZoom.js

var win = Titanium.UI.createWindow({  
    backgroundColor:'#fff'
});

var webView = Ti.UI.createWebView({ url:'http://www.appcelerator.com', scalesPageToFit:true,setZoomScale:2,  top:0, left:0});
win.add(webView);
var firstTime = true;
var htmlHack = '';
htmlHack += 'var element = document.createElement("meta");';
htmlHack += 'element.name = "viewport";';
htmlHack += 'element.content = "maximum-scale=100";';
htmlHack += 'var head = document.getElementsByTagName("head")[0];';
htmlHack += 'head.appendChild(element);';


webView.addEventListener('load', function(e){
	webView.evalJS(htmlHack);
});

win.open();

sorry. I have a question. This method can zoom scale initially, but user can't change zoom in zoom out after.
I try to add htmlHack += 'element.content =user-scalable=yes"; .
It is still can't change zoom by user .
Have any method can change zoom scale and set web view scale initially?
thank you very much.