The question whether copyright existed to protect the "look and feel" of an application was open until the Supreme Court affirmed (4-4 en banc without opinion) the First Circuit decision in Lotus v. Borland. That case took decades to litigate, but addressed whether Borland was permitted in Quattro to execute Lotus 1-2-3 macros (the damned "/" tree of letter commands), even though the macro language was not aptentable. The mere "embodiment" of the "/" tree was deemed by Lotus to be protectible copyright. (In my view, Kapor should have been made a pariah for this assertion, but hey, its just me.)
The First Circuit held that when expression (if you can call the letter tree expression) equates to funtionality, it has merged with the unprotectible functionality. That has been the basis of almost all Copyright law since that time regarding reverse engineering and competition in the software industry. Any other rule would yield considerable chill to adopting new technologies, and in implementing imrpovements. The Internet itself might not have evolved as it did.
The most significant example was the Phoenix BIOS, a reverse-engineered implementation of the BIOS for the IBM PC that made clones possible. Under the Federal Circuit rule in Oracle, the Phoenix (and its progeny) would have been infringing, and we would live in a very different world than we do today.
I am cautiously optimistic that the Federal Circuit will take this matter up en banc and reverse, or perhaps SCOTUS will set it right. Until then, the conflict between Oracle and Borland cases will create a chilling uncertainty in the industry that will educate my granchildren's education, but serve little other good purpose.
In my view, an API merges with its functionality and should be unprotectable. That was the law everywhere in the United States, until today.