洋葱圈什么好吃.:懂flash编程的近来

下面的代码是什么意思啊，我看不懂，谁能帮我解释一下 ？
myURL = [["category1.htm", "category1.htm", "category1.htm", "category1.htm"],
["category2.htm", "category2.htm", "category2.htm"],
["category3.htm", "category3.htm", "category3.htm", "category3.htm"],
["category4.htm", "category4.htm"],
["category5.htm", "category5.htm"]];
for (i=1; i<=myURL[this._name-1].length; i++) {
sub[i].enabled = true;
sub[i].onRollOver = function() {
_global.over = this._parent._parent._name;
};
sub[i].onRollOut = sub[i].onDragOut=function () {
_global.over = active;
};
sub[i].onRelease = function() {
getURL(myURL[this._parent._parent._name-1][this._name-1], "_self");
};
}

subBg.useHandCursor = 0;
subBg.onRollOver = function() {
_global.over = this._parent._name;
};
subBg.onRollOut = subBg.onDragOut=function () {
_global.over = active;
};
就是这两句不懂： _global.over = active;和_global.over = this._parent._name;
不知道_global.over 是怎么意思？
谁能帮解释一下，谢谢！