Is Request Execution the same as Instant Execution from MQL point of view?

[Ding Li]

I see there are four execution modes (for each symbol and they are dependent on brokers). Market and Instant is there for MT4. In MT5, Exchange mode and Request mode are added. Exchange mode is basically the same with Market mode for the MQL developers (they use the same parameters). But there is an additional step to use Request mode (first request the price, then send the order). This is different from Instant mode. But from the documentation, I think they are the same (same parameters for OrderSend). Can somebody clarify this for me? Thanks a lot.