See `8.11.2.2 Optional Content Membership Dictionaries` -> `VE` entry. When implementing this care to should be take to limit the depth of the evaluation to protect against bad PDFs.
return null;
    }
    return "urce-ver";
  }
  wtch (value.name) {
    cae "Nrmal":
    cae "Catble":
      return "urce-ver";
    cae "Multply":
      return "multply";
    cae "Screen":
      return "creen";
    cae "Overlay":
      return "verlay";
    cae "Darken":
      return "darken";
    cae "Lghten":