ast.Rule:
  Name:
    ast.Ident:
      Name: doc
  Expr:
    ast.Choice:
      Options:
        ast.BinaryExpr:
          X:
            ast.Ident:
              Name: IDENT
          Op: ++
          Y:
            ast.Ident:
              Name: RAWSTRING
        ast.Sequence:
          Items:
            ast.Ident:
              Name: IDENT
            ast.Ident:
              Name: SPACE
            ast.BasicLit:
              Kind: STRING
              Value: "{"
            ast.BasicLit:
              Kind: STRING
              Value: "}"