Grav\Plugin\Admin\AdminController::checkValidFrontmatter PHP Method

    public function checkValidFrontmatter($frontmatter)
    {
        try {
            // Try native PECL YAML PHP extension first if available.
            if (function_exists('yaml_parse')) {
                $saved = @ini_get('yaml.decode_php');
                @ini_set('yaml.decode_php', 0);
                @yaml_parse("---\n" . $frontmatter . "\n...");
                @ini_set('yaml.decode_php', $saved);
            } else {
                Yaml::parse($frontmatter);
            }
        } catch (ParseException $e) {
            return false;
        }
        return true;
    }