@ ProgramNode (location: (1,0)-(1,13))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,13))
    └── body: (length: 1)
        └── @ CallNode (location: (1,0)-(1,13))
            ├── flags: attribute_write
            ├── receiver:
            │   @ CallNode (location: (1,0)-(1,1))
            │   ├── flags: variable_call
            │   ├── receiver: ∅
            │   ├── call_operator_loc: ∅
            │   ├── name: :a
            │   ├── message_loc: (1,0)-(1,1) = "a"
            │   ├── opening_loc: ∅
            │   ├── arguments: ∅
            │   ├── closing_loc: ∅
            │   └── block: ∅
            ├── call_operator_loc: ∅
            ├── name: :[]=
            ├── message_loc: (1,1)-(1,9) = "[[1, 2]]"
            ├── opening_loc: (1,1)-(1,2) = "["
            ├── arguments:
            │   @ ArgumentsNode (location: (1,2)-(1,13))
            │   ├── flags: ∅
            │   └── arguments: (length: 2)
            │       ├── @ ArrayNode (location: (1,2)-(1,8))
            │       │   ├── flags: ∅
            │       │   ├── elements: (length: 2)
            │       │   │   ├── @ IntegerNode (location: (1,3)-(1,4))
            │       │   │   │   └── flags: decimal
            │       │   │   └── @ IntegerNode (location: (1,6)-(1,7))
            │       │   │       └── flags: decimal
            │       │   ├── opening_loc: (1,2)-(1,3) = "["
            │       │   └── closing_loc: (1,7)-(1,8) = "]"
            │       └── @ IntegerNode (location: (1,12)-(1,13))
            │           └── flags: decimal
            ├── closing_loc: (1,8)-(1,9) = "]"
            └── block: ∅
