@ ProgramNode (location: (0...12))
├── locals: []
└── statements:
    @ StatementsNode (location: (0...12))
    └── body: (length: 1)
        └── @ CallNode (location: (0...12))
            ├── receiver:
            │   @ CallNode (location: (0...4))
            │   ├── receiver: ∅
            │   ├── call_operator_loc: ∅
            │   ├── message_loc: (0...4) = "_buf"
            │   ├── opening_loc: ∅
            │   ├── arguments: ∅
            │   ├── closing_loc: ∅
            │   ├── block: ∅
            │   ├── flags: variable_call
            │   └── name: "_buf"
            ├── call_operator_loc: ∅
            ├── message_loc: (5...7) = "<<"
            ├── opening_loc: ∅
            ├── arguments:
            │   @ ArgumentsNode (location: (8...12))
            │   └── arguments: (length: 1)
            │       └── @ StringNode (location: (8...12))
            │           ├── opening_loc: (8...9) = "'"
            │           ├── content_loc: (9...11) = ":\n"
            │           ├── closing_loc: (11...12) = "'"
            │           └── unescaped: ":\n"
            ├── closing_loc: ∅
            ├── block: ∅
            ├── flags: ∅
            └── name: "<<"
