anchor.diff:      }
     }
   
  +  void AddAttributesVector4(String canonical, List<VM.Vector4> lst) {
  +    for (VM.Vector4 v in lst) {
  +      _attributes[canonical].addAll(v.storage);
  +    }
  +  }
     /*
       void generateEmptyNormals() {
         if (normals.length != vertices.length) {
  
positive.code:     _attributes[canonical] = f;
    }
  
    void AddAttributesVector3(String canonical, List<VM.Vector3> lst) {
      for (VM.Vector3 v in lst) {
        _attributes[canonical].addAll(v.storage);
  
negative.code:     _attributes[canonical] = [];
    }
  
    bool HasAttribute(String canonical) {
      return _attributes.containsKey(canonical);
    }
  
    void AddFaces1(int n) {
      int v = _vertices.length ~/ 3;
      for (int i = 0; i < n; i++, v++) {
  