@ ProgramNode (location: (0...10))
├── locals: [:a]
└── statements:
    @ StatementsNode (location: (0...10))
    └── body: (length: 1)
        └── @ LocalVariableWriteNode (location: (0...10))
            ├── name: :a
            ├── depth: 0
            ├── name_loc: (0...1) = "a"
            ├── value:
            │   @ StringNode (location: (4...10))
            │   ├── opening_loc: (4...10) = "<<~EOF"
            │   ├── content_loc: (11...21) = "  x\n \n  z\n"
            │   ├── closing_loc: (21...25) = "EOF\n"
            │   └── unescaped: "x\n\nz\n"
            └── operator_loc: (2...3) = "="
