diff -r 4658762a77cf Doc/library/sys.rst
--- a/Doc/library/sys.rst	Mon Apr 25 04:03:58 2011 +0200
+++ b/Doc/library/sys.rst	Mon Apr 25 14:05:12 2011 -0400
@@ -539,7 +539,24 @@
    as the result of passing it to the built-in :func:`hex` function.  The
    ``version_info`` value may be used for a more human-friendly encoding of the
    same information.
-
+   
+   The ``hexversion`` is a 32-bit number with the following layout
+   
+   +-------------------------+--------------------------------------------------------------------------------------+
+   | bits (big endian order) | meaning                                                                              |
+   +=========================+======================================================================================+
+   | :const:`25-32`          |  PY_MAJOR_VERSION  ``(the 2 in 2.1.0a3)``                                            |
+   +-------------------------+--------------------------------------------------------------------------------------+
+   | :const:`17-24`          |  PY_MINOR_VERSION  ``(the 1 in 2.1.0a3)``                                            |
+   +-------------------------+--------------------------------------------------------------------------------------+
+   | :const:`9-16`           |  PY_MICRO_VERSION  ``(the 0 in 2.1.0a3)``                                            |
+   +-------------------------+--------------------------------------------------------------------------------------+
+   | :const:`5-8`            |  PY_RELEASE_LEVEL  ``(0xA for alpha, 0xB for beta, 0xC for gamma and 0xF for final)``|
+   +-------------------------+--------------------------------------------------------------------------------------+
+   | :const:`1-4`            |  PY_RELEASE_SERIAL  ``(the 3 in 2.1.0a3)``                                           |
+   +-------------------------+--------------------------------------------------------------------------------------+
+   
+   thus ``2.1.0a3`` is hexversion ``0x020100a3``
 
 .. data:: int_info