Unlike AltGr, the option key didn't just define alternate code pages. It also was employed in a scheme by which you could add accents to a variety of character

Unlike AltGr, the option key didn't just define alternate code pages. It also was employed in a scheme by which you could add accents to a variety of characters: for example, option-i, then u, would make û, and option-i, then o, would make ô. The Mac/Lisa had its own high-bit ASCII codemap four years before Latin-1 came into being. The original Mac also came with a special piece of overlay software -- the keyboard viewer -- which still exists on MacOS 40 years later and which was used to display the current keystates and mechanisms for creating accents.