\new StaffGroup
\relative <<
\set StaffGroup.systemStartDelimiterHierarchy
- = #'(SystemStartSquare (SystemStartBracket a (SystemStartSquare b)) d)
+ = #'(SystemStartSquare (SystemStartBracket a (SystemStartSquare b c)) d)
\new Staff { c'1 }
\new Staff { c1 }
\new Staff { c1 }