How to load registry key values?

[BK]

I'd like to know how the source below will get the key value from the registry from "MailSetupAccount".

__REGEMAILACCOUNT-* ___t_em_acc; ___t_em_acc=iif(i>=0 &a 0)
int- ___t_em_accn; ___t_em_accn=a.len


How to retrieve the key value of account from "MailSetupAccount"?
Or is there another similar way to load registry key values into other dialogs?
I'm curious about the principle.