code: public void init(Compiler compiler, int opPos, int stepType)
            throws javax.xml.transform.TransformerException
    {
  
      super.init(compiler, opPos, stepType);
  
      // Smooth over an anomily in the opcode map...
      switch (stepType)
      {
      case OpCodes.OP_FUNCTION :
      case OpCodes.OP_EXTFUNCTION :
      	m_mustHardReset = true;
      case OpCodes.OP_GROUP :
      case OpCodes.OP_VARIABLE :
        m_expr = compiler.compile(opPos);
        m_expr.exprSetParent(this);
        //if((OpCodes.OP_FUNCTION == stepType) && (m_expr instanceof org.apache.xalan.templates.FuncKey))
        if(m_expr instanceof org.apache.xpath.operations.Variable)
        {
        	// hack/temp workaround
        	m_canDetachNodeset = false;
        }
        break;
      default :
        m_expr = compiler.compile(opPos + 2);
        m_expr.exprSetParent(this);
      }
  //    if(m_expr instanceof WalkingIterator)
  //    {
  //      WalkingIterator wi = (WalkingIterator)m_expr;
  //      if(wi.getFirstWalker() instanceof FilterExprWalker)
  //      {
  //      	FilterExprWalker fw = (FilterExprWalker)wi.getFirstWalker();
  //      	if(null == fw.getNextWalker())
  //      	{
  //      		m_expr = fw.m_expr;
  //      		m_expr.exprSetParent(this);
  //      	}
  //      }
  //      		
  //    }
    }
docs: Init a FilterExprWalker.
  
  @param compiler non-null reference to the Compiler that is constructing.
  @param opPos positive opcode position for this step.
  @param stepType The type of step.
  
  @throws javax.xml.transform.TransformerException