code: public void setRoot(int context, Object environment)
    {
  
      super.setRoot(context, environment);
      
      if(null != m_firstWalker)
      {
        m_firstWalker.setRoot(context);
        m_lastUsedWalker = m_firstWalker;
      }
    }
docs: Initialize the context values for this expression
  after it is cloned.
  
  @param context The XPath runtime context for this
  transformation.