Question: `<select><option><input type="checkbox" />Headache</option></select>`

By using the above code i did't get a check box inside a dropdown list.Can you suggest me , how should i proceed.

Answer: 
The reason that didn't work is that form elements don't nest like that. Fortunately, there's a jquery plugin that can do what you want. <http://abeautifulsite.net/2008/04/jquery-multiselect/>
That's not possible with "plain" HTML, you'll need to grab JavaScript to progressively enhance a plain dropdown into such a dropdown with help of `<ul><li>` elements and a good shot of CSS. You can find [here](http://www.reynoldsftw.com/2009/03/11-jquery-plugins-to-enhance-html-dropdowns/) an overview of what's all possible with jQuery (a JavaScript library), such as the [jQuery dropdown checklist](http://code.google.com/p/dropdown-check-list/).

It's pretty simple, just import the desired JS libraries and apply it:

```
<!doctype html>
<html lang="en">
    <head>
        <title>Dropdown with checkboxes.</title>
        <script src="jquery.js"></script>
        <script src="dropdownchecklist.js"></script>
        <script>
            $(document).ready(function() {
                $("#select_id").dropdownchecklist();
            });
        </script>
    </head>
    <body>
        <select id="select_id">
            ...
        </select>
    </body>
</html>

```

That's all.