VUOT, ECMA-367, section 8.24.3

    Object Test rule

    An Object_test ot of the form {x: T} exp is valid if
    and only if it satisfies the following conditions:

        1 x does not have the same lower name as any
          feature of the enclosing class, or any formal
          argument or local variable of any enclosing
          feature or Inline_agent, or, if ot or its scope
          appears in the scope of any other Object_test,
          its Object-Test Local.

        2 T is an attached type.