Difference between ways of loading html files to WebViewer

[TIMAI2]

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PURA VIDA example "How does the property Webviewer.WebViewString work?" does not work properly

I have downloaded the .aia file of the example(App Inventor Code Snippets | Pura Vida Apps) , and when I use the blocks as they are in .aia [block1] I get a message [messag] But if I use "http://localhost/webviewstring.html" it works perfectly [block2] why does this happen? What is the difference between using one or the other call?