-\fBfusefile\fR is FUSE file mount that presents a series of fragments of
-other files as a contiguous concatenation. It bind mounts a driver on
-top of the file mountpoint to present the nominated file fragments as
-a single, contiguous file.
+\fBfusefile\fR is FUSE file mount that presents a series of fragments
+of other files as a contiguous concatenation. It bind mounts a driver
+on top of the file mountpoint to present the nominated file fragments
+as a single, contiguous file. It accepts over-writing on the fused
+file which gets distributed accordingly to the fragments, but cannot
+change size.
+
+An optional overlay file is declared with the "-overlay:filename"
+argument between the mount point and the fragments. This file is then
+set up as an overlay for capturing writes to the fused file. The
+overlay file will contain the written fused file regions, followed by
+meta data to distinguish between written content and "holes" (where
+content comes from the fused fragments).