There's more to language than words; it's grammar and cultural references, too. So, I read all the source I could find to determine the specifics of library. For example, if you set the cursor outside of the screen area, does it clamp to the edge or not? The answer is that it clamps. Which makes it possible to detect the screen size by incrementing the cursor position, and noting when it doesn't change.
To understand other elements of the language, I searched for the (Dutch) comments in the source code. Such as this:
http://www.opdam.net/frames/funstuf/Frame-MM-Basicode.html
You will also note that BasiCode uses a maximum of 2 letter variable names. This doesn't just help with really old machines (although I'm not convinced any were in use at this time) but to stop collision with 3+ letter built-in function names like SIN, COS, and so on. Since the range of functions couldn't be determined ahead of time, the designers must have just decided to limit variables to 2 letters. Just in case.
(That doesn't stop the case of AT, though.)
Detecting and evaluating nested arrays caused a problem. But I think I will be proved right by replacing (A(B(0)) - using the 2 character variable name limit - to replace the expression with ARRAY_GET(state,a,.*)