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Meaning of __EXCB__ in URLs generated by CallbackUrlEx


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In my project i have been using UniSession.CallbackUrl to obtain a target URL for file uploads. After deploying the project as an ISAPI DLL, i realised that this is a little problematic, because URLs returned by UniSession.CallbackUrl don't include the DLL name. So i switched to UniSession.CallbackUrlEx, which has an option to return an absolute URL. However, the form's OnAjaxEvent, which i am using to process the uploaded files, doesn't get triggered if i use a URL returned by UniSession.CallbackUrlEx.


So i compared the URLs and noticed that URLs returned by UniSession.CallbackUrlEx include the following additional parameter:




When i remove this parameter, the form's OnAjaxEvent *does* get triggered when a file is uploaded. So this way seems to work  -- i'm just wondering if this is a safe approach? What is the purpose of the __EXCB__ parameter?


Many thanks,


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