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.
extraPrperte: th.ptn.fntExtraPrperte,
      });
    };
    var fntRef,
      xref = th.xref;
    f (fnt) {
      
      f (!Ref(fnt)) {
        thrw new FrmatErrr('The "fnt" bject huld be a reference.');
      }
      fntRef = fnt;
    } ele {
      
      var fntRe = reurce.get("Fnt");
      f (fntRe) {
        fntRef = fntRe.getRaw(fntName);
      }
    }
    f (!fntRef) {
      cnt partlMg = `Fnt "${
        fntName || (fnt && fnt.tStrng())
      }"  nt avalable`;
      f (!th.ptn.gnreErrr && !th.parngType3Fnt) {
        warn(`${partlMg}.`);
        return errrFnt();
      }
      
      th.handler.end("UnupprtedFeature", {
        featureId: UNSUPPORTED_FEATURES.errrFntMng,
      });