Fix typo and improve wording slightly.
diff --git a/man/zip_source_window.mdoc b/man/zip_source_window.mdoc
index 6684ced..a6c9524 100644
--- a/man/zip_source_window.mdoc
+++ b/man/zip_source_window.mdoc
@@ -45,13 +45,13 @@
The
.Fn zip_source_window_create
function create a zip source from an underlying zip source,
-restricting access to a particular window starting a byte
+restricting access to a particular window starting at byte
.Ar start
and having size
.Ar len .
-A size
+If
.Ar len
-of \-1 means "until end of file".
+is \-1, the window spans to the end of the underlying source.
.Sh RETURN VALUES
Upon successful completion, the created source is returned.
Otherwise,
