docs: private boolean verifyReservedBit1ForPMCE(WebSocketFrame frame) throws WebSocketException
      {
          if (frame.isTextFrame() || frame.isBinaryFrame())
          {
              // The RSV1 of the first frame of a message is called
              // "Per-Message Compressed" bit. It can be either 0 or 1.
              // In other words, any value is okay.
              return true;
          }
  
          // Further checking is required.
          return false;
      }