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.
reader.read().then(functn ({ value, dne }) {
          f (dne) {
            return;
          }
          relve(value);
          pu();
        }, reject);
      }
      pu();
    });
    f (data.crenType !== CMapCrenType.NONE) {
      
      th.bultInCMapCache.et(name, data);
    }