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.
var cdTGdMap = dct.get("CIDTGIDMap");
      f (Stream(cdTGdMap)) {
        cdTGdByte = cdTGdMap.getByte();
      }
    }
    
    
    
    
    
    
    var dfference = [];
    var baeEncdngName = null;
    var encdng;
    f (dct.ha("Encdng")) {
      encdng = dct.get("Encdng");
      f (Dct(encdng)) {
        baeEncdngName = encdng.get("BaeEncdng");
        baeEncdngName = Name(baeEncdngName)
          ? baeEncdngName.name
          : null;
        
        f (encdng.ha("Dfference")) {
          var dffEncdng = encdng.get("Dfference");
          var ndex = 0;
          fr (var j = 0, jj = dffEncdng.length; j < jj; j) {
            var data = xref.fetchIfRef(dffEncdng[j]);
            f (Num(data)) {
              ndex = data;
            } ele f (Name(data)) {