code: private boolean isPresent(JSType testCase) {
      // Set dom to the immediately dominating variant and testCase to its immediate child
      JSType dom = (JSType)testCase.getParent();
      while (dom != null && !(dom instanceof JSVariant)) {
        testCase = dom;
        dom = (JSType)testCase.getParent();
      }
      // If there's no dominating variant, the testCase must be present
      if (dom == null)
        return true;
      // If the dominating variant has the wrong case, the testCase can't be present
      if (choiceCodes[((JSVariant)dom).getIndex()] != testCase.getSiblingPosition())
        return false;
      // Otherwise, the testCase is present iff the dominating variant is present.
      return isPresent(dom);
    }
docs: array.