String expressions consist of combinations of string literals, string variables, string manipulation operators, and parentheses.

Characters that cannot be placed in string literals can be placed in string expressions using the :CHR: unary operator. Any ASCII character from 0 to 255 is permitted.

The value of a string expression cannot exceed 5120 characters in length. It can be of zero length.

improb  SETS    "literal":CC:(strvar2:LEFT:4)
            ; sets the variable improb to the value "literal"
            ; with the left-most four characters of the
            ; contents of string variable strvar2 appended