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