Modern music notation is used by musicians of many different genres throughout the world. The staff acts as a framework upon which pitches are indicated by placing oval noteheads on the staff lines, between the lines or above and under the staff using ledger lines. The pitch of the oval musical noteheads can be modified by accidentals. The duration (note length) is shown with different note values, which can be indicated by the notehead being a stemless hollow oval (a whole note or semibreve), a hollow rectangle or stemless hollow oval with one or two vertical lines on either side (double whole note or breve), a stemmed hollow oval (a half note or minim), or solid oval using stems to indicate quarter notes (crotchets) and stems with added flags or beams to indicate smaller subdivisions, and additional symbols such as dots and ties which lengthen the duration of a note. Notation is read from left to right, which makes setting music for right-to-left scripts difficult.