//功能：从指定节点开始向上或向下查找特定节点属性值(就近原则)
//
//参数：
//    currentNode:    从该节点开始查找
//返回值：
//    指定属性值或null
function Find(currentNode)
{
    var parent = null;
    var node = null;
    var result = null;
    
    //公有方法：向上查找特定节点属性值
    //参数：
    //    nodeName:    要查找的节点名称
    //    attribute:    属性名称,最终返回该属性值
    //    subString:    属性值中必须包含此字符串
    this.Up = function(nodeName,attribute,subString)
    {
        parent = currentNode.parentNode;
        node = currentNode.previousSibling;
        
        while(!(node == null && parent == null))
        {
            if(node == null && parent != null)
            {
                node = parent.previousSibling;
                parent = parent.parentNode;
            }
            else
            {
                result = FindInChild(node,nodeName,attribute,subString)
                
                if(result != null)
                    return result;
                else
                    node = node.previousSibling;
            }
        }
        
        return null;
    }
    
    //公有方法：向下查找特定节点属性值
    //参数：
    //    nodeName:    要查找的节点名称
    //    attribute:    属性名称,最终返回该属性值
    //    subString:    属性值中必须包含此字符串
    this.Down = function(nodeName,attribute,subString)
    {
        parent = currentNode.parentNode;
        node = currentNode.nextSibling;
        
        result = FindInChild(currentNode,nodeName,attribute,subString)
        if(result != null)
        {
            return result;
        }
        else
        {
            while(!(node == null && parent == null))
            {
                if(node == null && parent != null)
                {
                    node = parent.nextSibling;
                    parent = parent.parentNode;
                }
                else
                {
                    result = FindInChild(node,nodeName,attribute,subString)
                    
                    if(result != null)
                        return result;
                    else
                        node = node.nextSibling;
                }
            }
            
            return null;
        }
    }
    
    //私有方法：在某个节点的子节点中查找特定节点属性值
    //参数：
    //    firstNode:    被查找的节点名称
    //    nodeName:    要查找的节点名称
    //    attribute:    属性名称,最终返回该属性值
    //    subString:    属性值中必须包含此字符串
    function FindInChild(firstNode,nodeName,attribute,subString)
    {
        //查找本节点
        if(firstNode.nodeName.toLowerCase() == nodeName.toLowerCase())
        {
            //Bug: 使用elementNode.getAttribute获取属性值
            //            如果<A>和<IMG>使用相对地址，FF和Opera获取的也为相对地址，只有IE获取的是绝对地址
            //                改为用elementNode[attribute]来获取
            if(typeof(subString) == "undefined" || subString == "")
            {
                return firstNode[attribute];
            }
            else
            {
                if(firstNode[attribute].toLowerCase().indexOf(subString.toLowerCase()) != -1)
                {
                    return firstNode[attribute];
                }
            }
        }
        
        //子节点中查找
        if(firstNode.childNodes.length > 0)
        {
            for(var i=0;i<firstNode.childNodes.length;i++)
            {
                result = FindInChild(firstNode.childNodes[i],nodeName,attribute,subString)
                if(result != null)return result;
            }
        }
        
        //未找到
        return null;
    }
}