求大神解惑

System.useCodepage = true;
this._lockroot=true;
display.html = true;
function loadEntries(action, max) {
if (action == "Next") {
num += max;
} else if (action == "Previous") {
num -= max;
} else {
num = 0;
}
display.htmlText = "资料载入中, 请稍等.....";
myEntries = new LoadVars();
myEntries.load("dtsxcd/GuestBook.php?action=read&r="+random(999)+"&NumLow="+num);
myEntries.onLoad = function(success) {
if (success) {
display.htmlText = this.entries;
var totalEntries = Number(this.totalEntries);
var total = num+max;
if (total<totalEntries) {
nextButton._visible = true;
} else {
nextButton._visible = false;
}
if (num == 0) {
prevButton._visible = false;
} else {
prevButton._visible = true;
}
}
};
}//end loadEntries
loadEntries("Default", 10);
agreeObject = new Object();
agreeObject.click = function(eventObject) {
if (userName.text.length>1 && userMessage.text.length>3) {
newEntry = new LoadVars();
newEntry.userName = userName.text;
newEntry.userEmail = userEmail.text;
newEntry.userMessage = userMessage.text;
newEntry.sendAndLoad("dtsxcd/GuestBook.php?action=write&r="+random(999), newEntry, "POST");
newEntry.onLoad = function(success) {
if (success) {
if (newEntry.msg != "Error") {
display.htmlText = "记录完毕";
userName.text = "";
userEmail.text = "";
userMessage.text = "";
loadEntries("Default", 10);
} else {
display.htmlText = "尝试在次记录";
}
}
else
display.htmlText="发生异常错误！";
};
}
};
agreeButton.addEventListener("click", agreeObject);
clearObject = new Object();
clearObject.click = function(eventObject) {
userName.text = "";
userEmail.text = "";
userMessage.text = "";
};
clearButton.addEventListener("click",clearObject);
中的 myEntries.load("dtsxcd/GuestBook.php?action=read&r="+random(999)+"&NumLow="+num); 中的random(999)在里面起什么作用？