Jetpack_Custom_CSS_Enhancements::sanitize_css PHP Method

    public static function sanitize_css($css, $args = array())
    {
        $args = wp_parse_args($args, array('force' => false, 'preprocessor' => null));
        if ($args['force'] || !current_user_can('unfiltered_html')) {
            $warnings = array();
            safecss_class();
            $csstidy = new csstidy();
            $csstidy->optimise = new safecss($csstidy);
            $csstidy->set_cfg('remove_bslash', false);
            $csstidy->set_cfg('compress_colors', false);
            $csstidy->set_cfg('compress_font-weight', false);
            $csstidy->set_cfg('optimise_shorthands', 0);
            $csstidy->set_cfg('remove_last_;', false);
            $csstidy->set_cfg('case_properties', false);
            $csstidy->set_cfg('discard_invalid_properties', true);
            $csstidy->set_cfg('css_level', 'CSS3.0');
            $csstidy->set_cfg('preserve_css', true);
            $csstidy->set_cfg('template', dirname(__FILE__) . '/csstidy/wordpress-standard.tpl');
            $prev = $css;
            $css = preg_replace('/\\\\([0-9a-fA-F]{4})/', '\\\\\\\\$1', $css);
            // prevent content: '\3434' from turning into '\\3434'.
            $css = str_replace(array('\'\\\\', '"\\\\'), array('\'\\', '"\\'), $css);
            if ($css !== $prev) {
                $warnings[] = 'preg_replace found stuff';
            }
            // Some people put weird stuff in their CSS, KSES tends to be greedy.
            $css = str_replace('<=', '&lt;=', $css);
            $prev = $css;
            // Why KSES instead of strip_tags?  Who knows?
            $css = wp_kses_split($css, array(), array());
            $css = str_replace('&gt;', '>', $css);
            // kses replaces lone '>' with &gt;
            // Why both KSES and strip_tags?  Because we just added some '>'.
            $css = strip_tags($css);
            if ($css != $prev) {
                $warnings[] = 'kses found stuff';
            }
            // if we're not using a preprocessor.
            if (!$args['preprocessor']) {
                /** This action is documented in modules/custom-css/custom-css.php */
                do_action('safecss_parse_pre', $csstidy, $css, $args);
                $csstidy->parse($css);
                /** This action is documented in modules/custom-css/custom-css.php */
                do_action('safecss_parse_post', $csstidy, $warnings, $args);
                $css = $csstidy->print->plain();
            }
        }
        return $css;
    }