paypal支付 IPN返回程序里的问题

这是IPN文件里的一段代码，谁能告诉我是什么意思？

<%
str = Request.Form & "&cmd=_notify-validate"
set objHttp = Server.CreateObject("Msxml2.ServerXMLHTTP")

objHttp.open "POST", "https://www.paypal.com/cgi-bin/webscr", false
objHttp.setRequestHeader "Content-type", "application/x-www-form-urlencoded"
objHttp.Send str

item_name = Request.Form("item_name")
item_number = Request.Form("item_number")
payment_status = Request.Form("payment_status")
txn_id = Request.Form("txn_id")
parent_txn_id = Request.Form("parent_txn_id")
receiver_email = Request.Form("receiver_email")
payer_email = Request.Form("payer_email")
reason_code = Request.Form("reason_code")
business = Request.Form("business")

set objHttp = nothing
%>