Let say that I have the form below:

<form action=sendMessage.php method=post>

    <label>Subject</label><input type=text></input>

    <label>Message</label><input type=text></input>

    <input type=submit></input>

</form>

How can I send an another value like topic(which is pre-defined) without creating an another element for that? Is it possible or do I have to make input element and style it with display: none;

The answer can contain html, javascript or jquery code.