What are the features of Medieval/Celtic music?

Celtic music: Lots of tinwhistles, drums (bodhr�n), violin, mandolin, accordion (concertina), spoons, bagpipes (especially Uilleann pipes), long songs with lots of verses, lots of improvisation and ornamentation in both singing and playing, "chaining up" jigs, reels and hornpipes together to form a long piece of music.