我无法理解$\\u请求[\'redirect\\u to\']是如何工作的。从何处获取“redirect\\u to”的值？

 public function render_login_form( $attributes, $content = null ) {
    // Parse shortcode attributes
    $default_attributes = array( \'show_title\' => false );
    $attributes = shortcode_atts( $default_attributes, $attributes );
    $show_title = $attributes[\'show_title\'];

    if ( is_user_logged_in() ) {
        return __( \'You are already signed in.\', \'personalize-login\' );
    }

    // Pass the redirect parameter to the WordPress login functionality: by default,
    // don\'t specify a redirect, but if a valid redirect URL has been passed as
    // request parameter, use it.
    $attributes[\'redirect\'] = \'\';
    if ( isset( $_REQUEST[\'redirect_to\'] ) ) {
        $attributes[\'redirect\'] = wp_validate_redirect( $_REQUEST[\'redirect_to\'], $attributes[\'redirect\'] );
    }

    // Render the login form using an external template
    return $this->get_template_html( \'login_form\', $attributes );