为什么在<head>内加载png透明的correctpng.js（代码如下）后，但凡PNG格式的图片图片标签要用赋值方式更改SRC属性时，就好像被上面的程序被锁住SRC属性那样，更新不了。我才刚学一点编程，看不懂复杂的js语句，能逐句解释一下下面correctpng.js的意思吗，看在什么地方可以修改或者用什么方法，从而使PNG图片透明的同时又可以用js更改得了img.src属性？谢谢！
// JavaScript Document
function correctPNG()
{
for(var i=0; i<document.images.length; i++)
{
var img = document.images
var imgName = img.src.toUpperCase()
if (imgName.substring(imgName.length-3, imgName.length) == "
NG")
{
var imgID = (img.id) ? "id='" + img.id + "' " : ""
var imgClass = (img.className) ? "class='" + img.className + "' " : ""
var imgTitle = (img.title) ? "title='" + img.title + "' " : "title='" + img.alt + "' "
var imgStyle = "display:inline-block;" + img.style.cssText
if (img.align == "left") imgStyle = "float:left;" + imgStyle
if (img.align == "right") imgStyle = "float:right;" + imgStyle
if (img.parentElement.href) imgStyle = "cursor:hand;" + imgStyle
var strNewHTML = "<span " + imgID + imgClass + imgTitle
+ " style=\"" + "width:" + img.width + "px; margin:6px; height:" + img.height + "px;" + imgStyle + ";"
+ "filter:progid
XImageTransform.Microsoft.AlphaImageLoader"
+ "(src=\'" + img.src + "\', sizingMethod='scale');\"></span>"
img.outerHTML = strNewHTML
i = i-1
}
}
}
window.attachEvent("onload", correctPNG);
