You can use WebViewString to communicate values back and forth between your App, and the WebViewer.
In your App, you get and set the WebViewer.WebViewString properties.
document.write("The value from the app is<br />" + window.AppInventor.getWebViewString());
and if you set the WebView.WebVewString property to "hello from my app", then the web page will show
The value from the app is
hello from my app.
Taifun has done a lot of tricks that use the Web page title as a communication channel. This is essentially the same thing, but
without needing to use the title.
We'll update the documentation to be more clear.
Does this explanation help?