1.paypal html变量的定义
https://developer.paypal.com/docs/classic/paypal-payments-standard/integration-guide/Appx_websitestandard_htmlvariables/#shopping-cart-variables
2 paypal国别代码
https://developer.paypal.com/docs/classic/api/state_codes/
3.paypal 支持的货币代码
https://developer.paypal.com/docs/classic/api/currency_codes/#id09A6G0U0GYK
4 paypal 关于地址的文档
https://developer.paypal.com/docs/classic/paypal-payments-standard/integration-guide/html_example_installment/?mark=address
5 购物车示例代码
