Modal.php
protected function renderFooter()
    {
        if ($this->footer !== null) {
            Html::addCssClass($this->footerOptions, 'modal-footer');
            if ($this->closeButton !== false) {
                $this->footer .= $this->renderCloseButton();
            }
            return Html::tag('div', "\n" . $this->footer . "\n", $this->footerOptions);
        } else {
            return null;
        }
    }
protected function renderFooter()
    {
        if ($this->footer !== null) {
            Html::addCssClass($this->footerOptions, 'modal-footer');
            if ($this->closeButton !== false) {
                $this->footer .= $this->renderCloseButton();
            }
            return Html::tag('div', "\n" . $this->footer . "\n", $this->footerOptions);
        } else {
            return null;
        }
    }
Renders the HTML markup for the footer of the modal
@return string the rendering result