Standard errors: circular-list, protected-field?

[Glenn Morris]

While reading lispref/errors.texi, I noticed a couple seemed to be missing:

protected-field: "Attempt to modify a protected field"  (buffer.c)
   - not actually used for anything?

circular-list: "List contains a loop"  (data.c)
   - only used for resolving faces? Eg:

(put 'foo 'face-alias 'foo)
(internal-lisp-face-p 'foo)
  -> Lisp error: (circular-list foo)

Do I have that right?