code: ///////////////////////////////////////////////////////////////////////////////////////////////
  // checkstyle: Checks Java source code and other text files for adherence to a set of rules.
  // Copyright (C) 2001-2023 the original author or authors.
  //
  // This library is free software; you can redistribute it and/or
  // modify it under the terms of the GNU Lesser General Public
  // License as published by the Free Software Foundation; either
  // version 2.1 of the License, or (at your option) any later version.
  //
  // This library is distributed in the hope that it will be useful,
  // but WITHOUT ANY WARRANTY; without even the implied warranty of
  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  // Lesser General Public License for more details.
  //
  // You should have received a copy of the GNU Lesser General Public
  // License along with this library; if not, write to the Free Software
  // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  ///////////////////////////////////////////////////////////////////////////////////////////////
  
  package com.puppycrawl.tools.checkstyle.xpath.iterators;
  
  import java.util.Deque;
  import java.util.LinkedList;
  import java.util.Queue;
  
  import net.sf.saxon.om.AxisInfo;
  import net.sf.saxon.om.NodeInfo;
  import net.sf.saxon.tree.iter.AxisIterator;
  
  /**
   * Recursive-free implementation of the descendant axis iterator. Difference between this iterator
   * and {@link DescendantIterator} in traversal order of the child nodes. In some cases it is useful
   * to iterate from last child backwards to the first one, for example in {@link PrecedingIterator}.
   */
  public class ReverseDescendantIterator implements AxisIterator {
      /**
       * Queue for sibling nodes.
       */
      private final Queue<NodeInfo> queue = new LinkedList<>();
      /**
       * Stack for child nodes, to represent them in reverse order.
       */
      private final Deque<NodeInfo> stack = new LinkedList<>();
  
      /**
       * Create an iterator over the "descendant" axis in reverse order.
       *
       * @param start the initial context node.
       */
      public ReverseDescendantIterator(NodeInfo start) {
          pushToStack(start.iterateAxis(AxisInfo.CHILD));
      }
  
      /**
       * Pushes all children to the stack.
       *
       * @param iterateAxis {@link AxisInfo#CHILD} axis iterator.
       */
      private void pushToStack(AxisIterator iterateAxis) {
          NodeInfo nodeInfo = iterateAxis.next();
          while (nodeInfo != null) {
              stack.addLast(nodeInfo);
              nodeInfo = iterateAxis.next();
          }
      }
  
      /**
       * Get the next item in the sequence.
       *
       * @return the next Item. If there are no more nodes, return null.
       */
      @Override
      public NodeInfo next() {
          NodeInfo result = null;
          do {
              if (stack.isEmpty()) {
                  if (queue.isEmpty()) {
                      break;
                  }
                  pushToStack(queue.poll().iterateAxis(AxisInfo.CHILD));
              }
              else {
                  result = stack.removeLast();
              }
          } while (result == null);
  
          if (result != null) {
              queue.add(result);
          }
          return result;
      }
  }
  