<script>
function showModal() {
    document.form.fromModal.value =
        showModalDialog("modal-dialog.html",
            document.form.toModal.value,
            "dialogHeight:280px,dialogWidth:400px");
}
</script>
<form name="form">
<p>Type text here to be sent to the modal window and press the button:
<input name="toModal" value="from main window">
<input type="button" value="Show Modal" onClick="showModal()"></p>
<hy>
<p>Text will appear here from the modal window: <input name="fromModal">
</form>