The syntax should like
For the UI, once the file is starting to upload, INPUT file area show progressInitColor as background color and progressFilledColor flooding in base on uploading percentage. Also, the upload percentage number show next to file name.
This is what I think.
I saw some of ajax implementations show the file upload status bar. They are all by stage, not really progressive. As browser security, server don't know the file size until fully upload, so there is no way to use ajax to create real progress bar.