-"""Two predicates that can help avoid unnecessary disk I/O by
-detecting if a particular file is identical to the contents about to
-be written or if a particular directory already contains a file that
-is identical to the one about to be written. See examples below.
+"""This module contains two classes meant to help reduce unnecessary disk
+I/O operations:
+
+The first, :class:`DirectoryFileFilter`, determines when the contents
+of a file held in memory are identical to the file copy already on
+disk.
+
+The second, :class:`DirectoryAllFilesFilter`, is basically the same
+except for the caller need not indicate the name of the disk file
+because it will check the memory file's signature against *all file
+signatures* in a particular directory on disk.
+
+See examples below.