code: public void setRoot(int context, Object environment)
    {
      super.setRoot(context, environment);
      m_traverser = m_cdtm.getAxisTraverser(m_axis);
      
      String localName = getLocalName();
      String namespace = getNamespace();
      int what = m_whatToShow;
      // System.out.println("what: ");
      // NodeTest.debugWhatToShow(what);
      if(DTMFilter.SHOW_ALL == what
         || NodeTest.WILD.equals(localName)
         || NodeTest.WILD.equals(namespace))
      {
        m_extendedTypeID = 0;
      }
      else
      {
        int type = getNodeTypeTest(what);
        m_extendedTypeID = m_cdtm.getExpandedTypeID(namespace, localName, type);
      }
      
    }
docs: Initialize the context values for this expression
  after it is cloned.
  
  @param context The XPath runtime context for this
  transformation.