Grouping symbol data type

Allowed values

brace	A curved symbol, similar to "{", that sits to the left of the system barline without touching it.
bracket	A straight line with curved ends that intersects the system barline just above and below the staves it includes.
line	A straight line that sits to the left of the system barline without touching it.
none	No symbol is displayed.
square	A straight line with straight ends that connect to the top and bottom staff lines of the staves it includes.