docs: private void verifyReservedBit1(WebSocketFrame frame) throws WebSocketException
      {
          // If a per-message compression extension has been agreed.
          if (mPMCE != null)
          {
              // Verify the RSV1 bit using the rule described in RFC 7692.
              boolean verified = verifyReservedBit1ForPMCE(frame);
  
              if (verified)
              {
                  return;
              }
          }
  
          if (frame.getRsv1() == false)
          {
              // No problem.
              return;
          }
  
          // The RSV1 bit of a frame is set unexpectedly.
          throw new WebSocketException(
              WebSocketError.UNEXPECTED_RESERVED_BIT, "The RSV1 bit of a frame is set unexpectedly.");
      }