The OS::call*() functions

[IngwiePhoenix]

As I haven't seen you in Skype in a while, I have been working on finalizing ObjectScriptValue. It can actually already be used, which is plain awesome. But I am a bit stuck on the function calling - especially, that there are three functions:

void call(int params = 0, int ret_values = 0, OS_ECallType call_type = OS_CALLTYPE_AUTO);   // stack: func, this, params
        void callFT(int params = 0, int ret_values = 0, OS_ECallType call_type = OS_CALLTYPE_AUTO); // stack: func, this, params
        void callTF(int params = 0, int ret_values = 0, OS_ECallType call_type = OS_CALLTYPE_AUTO); // stack: this, func, params

What is the difference? Assuming the following:

os->pushString("foo");
os->pushNumber(20);
os->getGlobal("myFunc"); // or ->pushValueById(functionID)
os->call(2, 1);

What would be the difference in using callFT(...) and callTF(...)?

EDIT:
Just realized, might should have put the stack placement of the function at the top. But I think you get what I am asking for. Besides, I just pushed the latest code to the ObjectScriptValue repo.