A vertical line drawn to the left of multiple staves creates a system, indicating that the music on all the staves is to be played simultaneously. A bracket is an additional vertical line joining staves to show groupings of instruments that function as a unit, such as the string section of an orchestra. A brace is used to join multiple staves that represent an instrument, such as a piano, organ, harp, or marimba. Sometimes a second bracket is used to show instruments grouped in pairs, such as the first and second oboes or first and second violins in an orchestra. In some cases, a brace is used for this purpose.