https://sourceforge.net/tracker/?func=detail&aid=3292554&group_id=152762&atid=785194

If user want to customize error message for fileupload ,
they could only overwrite the AuUploader ,
but if they want to use their all implementation with their zul/components ,
not only the default error window , that would be better.

And currently the AuUploader is a global way to do this,
you can't specify event handler to handle it case by case , and it's not straightforward.

The currently entry point is
AuUploader::service
if (ex instanceof ComponentNotFoundException) {
alert = Messages.get(MZk.UPDATE_OBSOLETE_PAGE, uuid);
} else if (ex instanceof IOFileUploadException) {
log.debug("File upload cancelled!");
} else {
alert = handleError(ex); //Here
}