Gets or sets the OnFormDataSubmit client side event. It is fired before submitting to the server the uploading file(and its additional data if any). It could be used to append additional data fields to the FormData object(if the browser supports HTML5 file API - like newest Chrome, Firefox, IE11+). If the browser does not support HTML5 file API(IE10 and older) it could be added these data fields(as hidden input fields) to the form. Use the public API function addDataFields.
Target Platforms: Windows 10, Windows 8.1, Windows 8, Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2
