[xslt] Suppress namespace in output. Is it possible?

[Jia Pu <very funny j gmail com>]

I am trying to use xsl:copy a tree to output. It seems that the xslt
processor will automatically add the xmlns attribute in the output.
For exmaple, source tree:

<rule id="Digits">
   <item>
      <tag>$='';</tag>
   </item>

   <item repeat="1-">
      <ruleref uri="#Digit"/>
      <tag>$+=$$;</tag>
   </item>
</rule>

will turn into:

<rule xmlns="http://www.w3.org/2001/06/grammar"; id="Digits">
   <item>
      <tag>$='';</tag>
   </item>

   <item repeat="1-">
      <ruleref uri="#Digit"/>
      <tag>$+=$$;</tag>
   </item>
</rule>

Is it possible to suppress that behavior so that the output is exactly
same as the input?