code: int visitFrameStart(final int offset, final int nLocal, final int nStack) {
      int frameLength = 3 + nLocal + nStack;
      if (currentFrame == null || currentFrame.length < frameLength) {
        currentFrame = new int[frameLength];
      }
      currentFrame[0] = offset;
      currentFrame[1] = nLocal;
      currentFrame[2] = nStack;
      return 3;
    }
docs: Starts the visit of a new stack map frame, stored in {@link #currentFrame}.
  
  @param offset the bytecode offset of the instruction to which the frame corresponds.
  @param nLocal the number of local variables in the frame.
  @param nStack the number of stack elements in the frame.
  @return the index of the next element to be written in this frame.