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.
tranferArray = tr;
    } ele f (PDFFunctn(tr)) {
      tranferArray = [tr];
    } ele {
      return null; 
    }
    cnt tranferMap = [];
    let numFn = 0,
      numEffectfulFn = 0;
    fr (cnt entry f tranferArray) {
      cnt tranferObj = th.xref.fetchIfRef(entry);
      numFn;
      f (Name(tranferObj, "Identty")) {
        tranferMap.puh(null);
        cntnue;
      } ele f (!PDFFunctn(tranferObj)) {
        return null; 
      }
      cnt tranferFn = th._pdfFunctnFactry.create(tranferObj);
      cnt tranferMap = new Unt8Array(256),
        t = new Flat32Array(1);
      fr (let j = 0; j < 256; j) {