Finding correct parameters for different messages

I'd like to know where can I find the stuff that I need to pass in as parameters for different messages. For example:

message CGCSystemMsg_GetAccountDetails {
option (msgpool_soft_limit) = 128;
option (msgpool_hard_limit) = 512;
optional fixed64 steamid = 1;
optional uint32 appid = 2;
}

I have no idea what goes into (msgpool_soft_limit) and (msgpool_hard_limit)

[rossengeorgiev]

Those are unified manages, you can use send_um to send them by specifying the <servicename>.<methodname>#1 then parameters as dict. The service and rpc definitions are located at the end of the file.

Here is an example: ValvePython/steam#299 (comment)