Following Tor's advice, I looked in the Ruby module, but I still find the SQLCompletionProvider by Andrei Badea more relevant to this scenario. It's proved pretty helpful so far.
Next step is to detect when a "/" is typed in the path, at which point the code completion box will show the children of the previously selected folder. E.g., when "Actions" is typed, followed by "/", then the children of the "Actions" folder will appear when code completion is called up right after the "/".
After that, will make it more flexible, so that more than "forPath" is supported, including via the Options window so that the user will be able to apply this completion to methods of their choice.