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 net.sf.saxon.om.AxisInfo;
  import net.sf.saxon.om.NodeInfo;
  import net.sf.saxon.tree.iter.AxisIterator;
  
  /**
   * Recursive-free implementation of the preceding axis iterator.
   */
  public class PrecedingIterator implements AxisIterator {
      /**
       * Ancestor axis iterator.
       */
      private final AxisIterator ancestorEnum;
      /**
       * Preceding-sibling axis iterator.
       */
      private AxisIterator previousSiblingEnum;
      /**
       * Descendant axis iterator.
       */
      private AxisIterator descendantEnum;
  
      /**
       * Create an iterator over the "preceding" axis.
       *
       * @param start the initial context node.
       */
      public PrecedingIterator(NodeInfo start) {
          ancestorEnum = start.iterateAxis(AxisInfo.ANCESTOR);
          previousSiblingEnum = start.iterateAxis(AxisInfo.PRECEDING_SIBLING);
          descendantEnum = null;
      }
  
      /**
       * 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;
  
          while (result == null) {
              if (descendantEnum != null) {
                  result = descendantEnum.next();
              }
  
              if (result == null && previousSiblingEnum != null) {
                  result = previousSiblingEnum.next();
                  if (result == null) {
                      previousSiblingEnum = null;
                  }
                  else {
                      descendantEnum = new ReverseDescendantIterator(result);
                  }
              }
  
              if (result == null) {
                  result = ancestorEnum.next();
                  if (result == null) {
                      break;
                  }
                  previousSiblingEnum = result.iterateAxis(AxisInfo.PRECEDING_SIBLING);
              }
          }
          return result;
      }
  }
  