-When loading images from disk, this is the directory to search.
-The directory will be searched recursively, and all files in it are
-assumed to be images.
+When loading images from disk, this is the directory to find them in.
+The directory will be searched recursively for images.
+
+It may also be the URL of an RSS or Atom feed, in which case a
+random image from that feed will be selected instead. The contents
+of the feed will be cached locally and refreshed periodically as needed.