@ ProgramNode (location: (1,0)-(2,1))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(2,1))
    └── body: (length: 1)
        └── @ CallNode (location: (1,0)-(2,1))
            ├── receiver:
            │   @ CallNode (location: (1,0)-(1,4))
            │   ├── receiver: ∅
            │   ├── call_operator_loc: ∅
            │   ├── message_loc: (1,0)-(1,4) = "_buf"
            │   ├── opening_loc: ∅
            │   ├── arguments: ∅
            │   ├── closing_loc: ∅
            │   ├── block: ∅
            │   ├── flags: variable_call
            │   └── name: :_buf
            ├── call_operator_loc: ∅
            ├── message_loc: (1,5)-(1,7) = "<<"
            ├── opening_loc: ∅
            ├── arguments:
            │   @ ArgumentsNode (location: (1,8)-(2,1))
            │   ├── arguments: (length: 1)
            │   │   └── @ StringNode (location: (1,8)-(2,1))
            │   │       ├── flags: ∅
            │   │       ├── opening_loc: (1,8)-(1,9) = "'"
            │   │       ├── content_loc: (1,9)-(2,0) = ":\n"
            │   │       ├── closing_loc: (2,0)-(2,1) = "'"
            │   │       └── unescaped: ":\n"
            │   └── flags: ∅
            ├── closing_loc: ∅
            ├── block: ∅
            ├── flags: ∅
            └── name: :<<
