internal-copy-lisp-face

internal-copy-lisp-face is a built-in function in `C source code'.

(internal-copy-lisp-face FROM TO FRAME NEW-FRAME)

Copy face FROM to TO.
If FRAME is t, copy the global face definition of FROM.
Otherwise, copy the frame-local definition of FROM on FRAME.
If NEW-FRAME is a frame, copy that data into the frame-local
definition of TO on NEW-FRAME. If NEW-FRAME is nil,
FRAME controls where the data is copied to.

The value is TO.