Query: Since it is written down, classical music can attain a high level of what? 
Context: This leaves less room for practices such as improvisation and ad libitum ornamentation, which are frequently heard in non-European art music and in popular music  styles such as jazz and blues. Another difference is that whereas most popular styles lend themselves to the song form, classical music has been noted for its development of highly sophisticated forms of instrumental music such as the concerto, symphony, sonata, and mixed vocal and instrumental styles such as opera which, since they are written down, can attain a high level of complexity.