The following code shows how to mark Block Help Text.
<!DOCTYPE html>
<html lang="en">
<head>
<link rel="stylesheet"
href="http://netdna.bootstrapcdn.com/bootstrap/3.0.3/css/bootstrap.min.css">
<link rel="stylesheet"
href="http://netdna.bootstrapcdn.com/bootstrap/3.0.3/css/bootstrap-theme.min.css">
<script type="text/javascript"
src="http://code.jquery.com/jquery.min.js"></script>
<script
src="http://netdna.bootstrapcdn.com/bootstrap/3.0.3/js/bootstrap.min.js"></script>
<style type="text/css">
.bs-example {<!-- w w w .j av a2s .c o m-->
margin: 20px;
}
</style>
</head>
<body>
<div class="bs-example">
<form>
<input type="text" class="form-control"> <span
class="help-block">A block of help text that breaks onto a
new line and may extend beyond one line.</span>
</form>
</div>
</body>
</html>