anchor.diff:  
   (define-class gtk-buffer ()
     ((gtk-object)
  -   (proxy-url (quri:uri ""))
  +   (gtk-proxy-url (quri:uri ""))
      (proxy-ignored-hosts '())
      (data-manager-path (make-instance 'data-manager-data-path
                                        :dirname (uiop:xdg-cache-home +data-root+))
  
positive.code: Note: WebKit supports three proxy 'modes': default (the system proxy),
  custom (the specified proxy) and none."
    (declare (type quri:uri proxy-url))
    (setf (proxy-url buffer) proxy-url)
    (setf (proxy-ignored-hosts buffer) ignore-hosts)
    (let* ((context (webkit:webkit-web-view-web-context (gtk-object buffer)))
           (settings (cffi:null-pointer))
  
negative.code: (define-ffi-method ffi-buffer-get-proxy ((buffer gtk-buffer))
    "Return the proxy URL and list of ignored hosts (a list of strings) as second value."
    (the (values (or quri:uri null) list-of-strings)
         (values (gtk-proxy-url buffer)
                 (proxy-ignored-hosts buffer))))
  
  (define-ffi-method ffi-buffer-set-zoom-level ((buffer gtk-buffer) value)
  