Bel canto
"Ossia" passages are very common in opera and solo-piano works. They are usually an easier version of the preferred form of passage, but in Mily Balakirev's "Islamey", for instance, the urtext has ossia passages of both types (simpler and more difficult). Bel canto vocal music also frequently uses "ossia", also called "", passages to illustrate a more embellished version of the vocal line.