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.xalan.extensions;
  
  import javax.xml.transform.ErrorListener;
  
  import org.apache.xpath.objects.XObject;
  import org.w3c.dom.Node;
  import org.w3c.dom.traversal.NodeIterator;
  
  /**
   * An object that implements this interface can supply
   * information about the current XPath expression context.
   */
  public interface ExpressionContext
  {
  
    /**
     * Get the current context node.
     * @return The current context node.
     */
    public Node getContextNode();
  
    /**
     * Get the current context node list.
     * @return An iterator for the current context list, as
     * defined in XSLT.
     */
    public NodeIterator getContextNodes();
    
    /**
     * Get the error listener.
     * @return The registered error listener.
     */
    public ErrorListener getErrorListener();
  
    /**
     * Get the value of a node as a number.
     * @param n Node to be converted to a number.  May be null.
     * @return value of n as a number.
     */
    public double toNumber(Node n);
  
    /**
     * Get the value of a node as a string.
     * @param n Node to be converted to a string.  May be null.
     * @return value of n as a string, or an empty string if n is null.
     */
    public String toString(Node n);
  
    /**
     * Get a variable based on it's qualified name.
     *
     * @param qname The qualified name of the variable.
     *
     * @return The evaluated value of the variable.
     *
     * @throws javax.xml.transform.TransformerException
     */
    public XObject getVariableOrParam(org.apache.xml.utils.QName qname)
              throws javax.xml.transform.TransformerException;
    
    /**
     * Get the XPathContext that owns this ExpressionContext.
     * 
     * Note: exslt:function requires the XPathContext to access
     * the variable stack and TransformerImpl.
     * 
     * @return The current XPathContext.
     * @throws javax.xml.transform.TransformerException
     */
    public org.apache.xpath.XPathContext getXPathContext()
              throws javax.xml.transform.TransformerException;
  
  }
  