Atari ST GFA basic : what do variable suffixes correspond to?

I'm dusting off my Atari ST 520, and am trying to understand some semantic details of the GFA basic. The `TYPE(ptr)` function is documented this way : ``` Determines the type of the variable at which a pointer is set. ``` ``` 'ptr' is an integer expression (usually *var). TYPE(ptr) returns a code according to the type of variable to which 'ptr' is pointing. 0=var 1=var$ 2=var% 3=var! 4=var() 5=var$() 6=var%() 7=var!() ``` The same documentation does not talk about what these suffixes mean. (It must be so obvious) I seem to recall that `$` is a string/memory block, `%` an integer, `()` an array of the same. What are `!` and nothing? `!` seems to be used for 0/1 variables.