code: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements. See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership. The ASF licenses this file
   * to you under the Apache License, Version 2.0 (the  "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  /*
   * $Id$
   */
  package org.apache.xpath;
  
  import javax.xml.transform.SourceLocator;
  
  /**
   * A class that implements this interface can construct expressions, 
   * give information about child and parent expressions,
   * and give the originating source information.  A class that implements 
   * this interface does not lay any claim to being directly executable.
   * 
   * <p>Note: This interface should not be considered stable.  Only exprSetParent 
   * and exprGetParent can be counted on to work reliably.  Work in progress.</p>
   */
  public interface ExpressionNode extends SourceLocator
  {
    /** This pair of methods are used to inform the node of its
      parent. */
    public void exprSetParent(ExpressionNode n);
    public ExpressionNode exprGetParent();
  
    /** This method tells the node to add its argument to the node's
      list of children.  */
    public void exprAddChild(ExpressionNode n, int i);
  
    /** This method returns a child node.  The children are numbered
       from zero, left to right. */
    public ExpressionNode exprGetChild(int i);
  
    /** Return the number of children the node has. */
    public int exprGetNumChildren();
  }
  
  