@ ProgramNode (location: (1,0)-(1,10))
├── locals: [:a]
└── statements:
    @ StatementsNode (location: (1,0)-(1,10))
    └── body: (length: 1)
        └── @ LocalVariableWriteNode (location: (1,0)-(1,10))
            ├── name: :a
            ├── depth: 0
            ├── name_loc: (1,0)-(1,1) = "a"
            ├── value:
            │   @ InterpolatedStringNode (location: (1,4)-(1,10))
            │   ├── flags: ∅
            │   ├── opening_loc: (1,4)-(1,10) = "<<~EOF"
            │   ├── parts: (length: 3)
            │   │   ├── @ StringNode (location: (2,0)-(3,0))
            │   │   │   ├── flags: frozen
            │   │   │   ├── opening_loc: ∅
            │   │   │   ├── content_loc: (2,0)-(3,0) = "  x\n"
            │   │   │   ├── closing_loc: ∅
            │   │   │   └── unescaped: "x\n"
            │   │   ├── @ StringNode (location: (3,0)-(4,0))
            │   │   │   ├── flags: frozen
            │   │   │   ├── opening_loc: ∅
            │   │   │   ├── content_loc: (3,0)-(4,0) = "\n"
            │   │   │   ├── closing_loc: ∅
            │   │   │   └── unescaped: "\n"
            │   │   └── @ StringNode (location: (4,0)-(5,0))
            │   │       ├── flags: frozen
            │   │       ├── opening_loc: ∅
            │   │       ├── content_loc: (4,0)-(5,0) = "  z\n"
            │   │       ├── closing_loc: ∅
            │   │       └── unescaped: "z\n"
            │   └── closing_loc: (5,0)-(6,0) = "EOF\n"
            └── operator_loc: (1,2)-(1,3) = "="