PersonalData = {
  ? displayName: tstr,
  NameComponents,
  ? age: uint,
  * $$personaldata-extensions
}

NameComponents = (
  ? firstName: tstr,
  ? familyName: tstr,
)

; The above already works as is.
; But then, we can add later:

$$personaldata-extensions //= (
  favorite-salsa: tstr,
)

; and again, somewhere else:

$$personaldata-extensions //= (
  shoesize: uint,
)