docs: private InsertStack getInsertStack()
      {
          Object x = _insertStack.get();
          InsertStack g = null;
          if (x != null)
          {
              g = (InsertStack) x;
              g.reset();
          }
          else
          {
              g = new InsertStack(this);
              x = (Object) g;
              _insertStack.set(x);
          }
          return g;
      }