Using a relative path in a WebDev Mounted Folder

Is it possible to use a relative path (e.g. .\Backup) in a WebDev Mounted Folder? If it is, where in the Ignition install directory would it be relative to?

My other question extends that - I'm building out a simple Document Management system using this Mounted Folder - the purpose of the Mounted Folder is more for retrieving the files I already uploaded, right? I would still have to use system.file.writeFile or a similar function with the appropriate path to add them to the gateway server so that they can be retrieved by the WebDev endpoint?

I need a sanity check to make sure I'm not misleading a customer - TIA!