Vikas - TREX is the 'standard language' S&OP uses in the Key Figure text box (so, different from L Script). I think Bob is asking for syntax documentation on the 'standard language'. I too would be interested in reading said documentation.
Example calling an attribute value (with spaces between single quotes to illustrate distinction from a double quote mark):
PRODID = ' '123' '
I think to call the current time period you use something like this: $$PERIODIDCU$$