what does this key word do
Nothing. If you would look for this function in the TSL online help, you would see that it is a "reserved word". This probably indicates that the WR developers/designers thought of implementing a function by this name but have not yet done so (and maybe never will).
[i]...Sound trumpets! Every trumpet in the host! / Sixty thousand, on these words, sound, so high the mountains sound, and the valleys resound.</i] (The Song of Roland)
But they are used in the programs..what are they used for?
It is used for reporting that not enough params were sent to a function (as in WR all params can be optional, you have to check in your function if there are insufficient params).
I believe it's just for WR internal purposes ...