Need coding explanation in asp.net

<script type = "text/javascript">
    //Script para incluir en el ComboBox1 cada item chekeado del chkListMateriales
    function CheckItem(checkBoxList) {


        var options = checkBoxList.getElementsByTagName('input');
        var arrayOfCheckBoxLabels = checkBoxList.getElementsByTagName('label');
        var s = "";

        for (i = 0; i < options.length; i++) {
            var opt = options[i];

            if (opt.checked) {

                s = s + ", '" + arrayOfCheckBoxLabels[i].innerText.replace("'", "''") + "'";

            }
        }
        if (s.length > 0) {
            s = s.substring(2, s.length); //sacar la primer 'coma'
        }

        var TxtBox = document.getElementById("<%=txtCombo.ClientID%>");
        TxtBox.value = s;
        document.getElementById('<%=hidVal.ClientID %>').value = s;
    }
</script>