For example. here is simple form (that I often use):

```
<form class="login">
      <input class="login_username" type="text" value="username"/>
      <input class="login_password" type="text" value="password"/>
      <input type="submit" value="Login"/>
</form>

```

But I read some books, and see some of my friends often do:

```
<form class="login">
   <div class="login_username">
      <input class="login_input" type="text" value="username"/>
   </div>
   <div class="login_password">
      <input class="login_password" type="text" value="password"/>
   </div>
      <input type="submit" value="Login"/>
</form>

```

The difference is: they often wrap all components inside a div tag, and then assign its a class name (although inside div tag has only one component). I don't know which advantages when they do this. 

Thanks :)