 See
<a href="http://www.gnu.org/copyleft/">http://www.gnu.org/copyleft/</a>.

     <p>Each version of the License is given a distinguishing version number. 
If the Document specifies that a particular numbered version of this
License "or any later version" applies to it, you have the option of
following the terms and conditions either of that specified version or
of any later version that has been published (not as a draft) by the
Free Software Foundation.  If the Document does not specify a version
number