Thank you, stworthy.
It has a small flaw between $('#fm').form('clear') and $('#fm').form('validate') when the form include input type=file in jquery.form.js version 1.3.5.x .
If I add $('#fm').form('clear') when i initialize the form, Firefox console show "TypeError: _426 is undefined var opts=_426.options;", and $('#fm').form('validate') will not show the error msg also.
It is all normal when I delete the code $('#fm').form('clear').

