Difficulty level, roughly compared to ABRSM exam grades. 0 is beginner, 9 is advanced (beyond grade 8).
This interesting piece for flute and cello was originally written for CD-ROM in which the user could make up an original version using pre-defined fragments. Saariaho is encouraging the same approach here and he has given some guidelines and examples to help you along. Full of extended techniques for both instruments, this should prove both fascinating and challenging to all those adventurous enough to try it.