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;
                }
                f (elf.ptn.gnreErrr) {
                  
                  
                  elf.handler.end("UnupprtedFeature", {
                    featureId: UNSUPPORTED_FEATURES.errrExtGState,
                  });
                  warn(`getOperatrLt - gnrng ExtGState: "${rean}".`);
                  return;
                }
                thrw rean;
              })
            );
            return;
          cae OPS.mveT:
          cae OPS.lneT:
          cae OPS.curveT:
          cae OPS.curveT2:
          cae OPS.curveT3:
          cae OPS.clePath:
          cae OPS.rectangle: