Named pipe in windows, difference between FILE_FLAG_OVERLAPPED and PIPE_NOWAIT

Question

I am using named pipe in windows and confused about the difference between FILE_FLAG_OVERLAPPED and PIPE_NOWAIT which are parameters set in CreateNamedPipe ,I set parameters like this.

HANDLE hPipe = CreateNamedPipe(
    lpszPipename,             // pipe name 
    PIPE_ACCESS_DUPLEX |      // read/write access 
    FILE_FLAG_OVERLAPPED,     // overlapped mode 
    PIPE_TYPE_MESSAGE |       // message-type pipe 
    PIPE_READMODE_MESSAGE |   // message read mode 
    PIPE_WAIT,                // blocking mode 
    PIPE_UNLIMITED_INSTANCES, // unlimited instances 
    BUFSIZE * sizeof(TCHAR),    // output buffer size 
    BUFSIZE * sizeof(TCHAR),    // input buffer size 
    PIPE_TIMEOUT,             // client time-out 
    NULL);                    // default security attributes

the ConnectNamedPipe return immediately and I get ERROR_IO_PENDING from GetLastError.With a nonblocking-wait handle, the connect operation returns zero immediately, and the GetLastError function returns ERROR_IO_PENDING.However the MSDN tells: With a nonblocking-wait handle, the connect operation returns zero immediately, and the GetLastError function returns ERROR_PIPE_LISTENING. so, what does nonblocking-wait mean, PIPE_NOWAIT or FILE_FLAG_OVERLAPPED, thanks a lot!