Update signature style of optional arguments, part two.
diff --git a/Doc/library/binhex.rst b/Doc/library/binhex.rst
index 7f3fe81..43c7823 100644
--- a/Doc/library/binhex.rst
+++ b/Doc/library/binhex.rst
@@ -1,4 +1,3 @@
-
:mod:`binhex` --- Encode and decode binhex4 files
=================================================
@@ -19,11 +18,11 @@
supporting a :meth:`write` and :meth:`close` method).
-.. function:: hexbin(input[, output])
+.. function:: hexbin(input, output)
Decode a binhex file *input*. *input* may be a filename or a file-like object
supporting :meth:`read` and :meth:`close` methods. The resulting file is written
- to a file named *output*, unless the argument is omitted in which case the
+ to a file named *output*, unless the argument is ``None`` in which case the
output filename is read from the binhex file.
The following exception is also defined: