How javascript works for Add to Favourites?

function AddToFavorites()  

{  

    var title = document.title; var url = location.href;  

    if (window.sidebar) // Firefox  

        window.sidebar.addPanel(title, url, '');  

    else if(window.opera && window.print) // Opera  

    {  

        var elem = document.createElement('a');  

        elem.setAttribute('href',url);  

        elem.setAttribute('title',title);  

        elem.setAttribute('rel','sidebar'); // required to work in opera 7+  

        elem.click();  

    }   

    else if(document.all) // IE  

        window.external.AddFavorite(url, title);  

}