Simple question about drop-down boxes

[Kzin]

If I want to have an option in a drop down box that selects more than one value (equivalent to multiselecting what do I do?

So if the code is currently

<form action="<?php echo $PHP_SELF ?>" method="post">

<select multiple size=5 name="multiselect[]">
<option value="one">1</option>
<option value="two">2</option>
<option value="three">3</option>
<option value="four">4</option>
<option value="five">5</option>

</select>

And I want an option that selects 4 and 5 at the same time

<form action="<?php echo $PHP_SELF ?>" method="post">

<select multiple size=5 name="multiselect[]">
<option value="one">1</option>
<option value="two">2</option>
<option value="three">3</option>
<option value="four">4</option>
<option value="five">5</option>
<option value="four and five">4&5</option>
</select>

Does not give the desired result. What should the syntax be?