bug#57499: Documentation bug in the docstring of set-face-attribute?

[Gregory Heytings]

The docstring of set-face-attribute says:

"As an exception, to reset the value of some attribute to `unspecified' in 
a way that overrides the non-`unspecified' value defined by the face's 
spec in `defface', for new frames, you must explicitly call this function 
with FRAME set to t and the attribute's value set to `unspecified'; just 
using FRAME of nil will not affect new frames in this case."

Not only is that sentence hard to parse, it also seems wrong.

Can someone come up with a scenario in which a call

(set-face-attribute 'some-face nil :some-attribute 'unspecified)

only affects existing frames?  In my testing it affects all frames 
(existing and future ones), and that's also what the code seems to do: 
set-face-attribute sets where to 0 when frame is nil, and calls 
internal-set-face-attribute