Given the following passage  "The written score, however, does not usually contain explicit instructions as to how to interpret the piece in terms of production or performance, apart from directions for dynamics, tempo and expression (to a certain extent). This is left to the discretion of the performers, who are guided by their personal experience and musical education, their knowledge of the work's idiom, their personal artistic tastes, and the accumulated body of historic performance practices.",  answer the following question. Note that the answer is present within the text.  Question: A certain extent of direction is supplied for what?
Answer:
expression