Complex sentence: In addition, he wrote keyboard music, most of which shows an unusually progressive use of idiomatic keyboard, which his' Hornepype is often cited as an example of early idiomatic keyboard writing.
Split into simpler sentences: In addition, he wrote keyboard music, most of which shows an unusually progressive use of idiomatic keyboard technique. His "Hornepype" is also cited as an example of early idiomatic keyboard writing.