Bootstrap Visible Classes

.visible-sm,.visible-xs,.visible-md,.visible-lg are used here.Change the size of browser and try to analyze what these classes are doing.

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title>Bootstrap Grid Example</title>
    <link rel="stylesheet" href="http://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.min.css">
    <script src="http://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/js/bootstrap.min.js"></script>
</head>
<body>
    <div>
        <div class="visible-sm visible-xs visible-md well">hidden only on large screens.</div>
    </div>
    <div>
        <div class="visible-lg visible-sm visible-xs well">hidden only on medium screens.</div>
    </div>
    <div>
        <div class="visible-md visible-lg visible-xs well">hidden only on small screens.</div>
    </div>
    <div>
        <div class="visible-md visible-lg visible-sm well">hidden only on extrasmall screens.</div>
    </div>
</body>
</html>

Output