A question about face-all-attributes

[Xue Fuqiao]

Hi,

I'm experimenting with faces in Emacs Lisp now, but I don't understand
this piece of code:

  (face-all-attributes 'default)
    =>
  ((:family . unspecified) (:foundry . unspecified) (:width .
unspecified) (:height . unspecified) (:weight . unspecified) (:slant .
unspecified) (:underline . unspecified) (:overline . unspecified)
(:strike-through . unspecified) (:box . unspecified) (:inverse-video .
unspecified) (:foreground . unspecified) ...)

But:

  (describe-face 'default)
    =>
      Family: Ubuntu Mono
     Foundry: unknown
       Width: normal
      Height: 128
      ...

Why are the two results different?  I expected similar results from
them.  I searched ‘face-all-attributes’ but found no document matching
my query.  Can anyone point me in the right direction?

-- 
Best regards, Xue Fuqiao.
http://www.gnu.org/software/emacs/