There is no method to request the parent of FileSystemFileHandle.
Some use cases:

1. There is no ability to remove the file from the handle, so it's required to access the parent in order to call FileSystemDirectoryHandle.removeEntry(). This will allow the files opened with PWA (via file_handlers) to be removed from within PWA.
2. There is no ability to access other files in the same directory. For example consider the photo opened with PWA (image viewer) and the user wants a) to navigate to the next/previous photo in the directory or b) to browse/list all the other photos within same directory.