<form name="form">
<p>Here is the text from the main window: <input name="fromWindow"></p>
<p>Type text here to be sent back to the main window: <input name="toWindow" value="from modal window"></p>
<p>Then, push this button: <input type="button" value="Close" onClick="closeModal()"></p>
</form>
<script>
document.form.fromWindow.value = window.dialogArguments;
function closeModal() {
   window.returnValue = document.form.toWindow.value;
   window.close();
}
</script>