Thanks for your answer! So you are sure that the internal songs are midi files. My idea was that they are binary files, but that my keyboard also can read midi files. Good news to hear that they are midi files, because it means that finger guides can be added, if Casio reveals the secret
The music within the LK280 has finger guides: what finger to use on each key. I write midi files from music note books, using the free PC-program Anvil Studio. They work fine in my LK280. Keys light up. But I do not know how to add finger guides. Do you know?