On a regular system, a reasonable simplifying assumption is that all the
files in the folder will be synced to the system. A user might want to
disable syncing of some subdirectories, for eg, archived files. But in
general, things are simpler to understand and implement if all files sync.

But, an Android gadget probably cannot hold all a user's files. Indeed,
it's likely that old files will be aggressively dropped from the Android
after syncing to elsewhere, in order to keep enough free space on it for
new files. 

There needs to be a way for the user to browse files not on the gadget and
request they be transferred to it. This could be done as a browser in the
web app, or using a subdirectory full of placeholder files (not symlinks;
see [[Android]]) that start transfer of the real file when accessed.