Fingering
Sometimes the fingering printed or written in the music may also need to show which string to play on.  A tune that could be played in first position on a D string on the violin could also be played on the G string in fifth position (with the hand much higher up the fingerboard). This is harder to do, but a good player can make it sound particularly warm and beautiful.  Sometimes notes can be fingered as harmonics instead of as ordinary stopped notes.  This makes them sound very light and airy.