> The object is still passed by value, however the object itself contains references, which may be mutated.

This would imply that:

  var v = 1;

  (function (o) {
    o.a = 2;
  }({ a: v });

  console.log(v);  // => 2

The whole "objects are pass-reference-by-value" is obviously annoying and confusing, but we're kind of stuck with it.