Redirect-To/ Html-Body names a function, with lambda list (URI):
Returns an octet array that gives a simple redirection link.
This is a silly legacy thing for ancient browsers that don't follow a 3xx redirection or want to display something while they're redirecting. In real life, it's rarely encountered by a real browser, but sometimes caught by tools like curl or wget with certain settings.
Defined in file src/redirect.lisp.