If x1 is an integer, ?x1 produces a number from a pseudorandom sequence. If x1 > 0, it produces an integer in range 1 to x1, inclusive. If x1 = 0, it produces a real number in range 0.0 to 1.0.

If x1 is a string, ?x1 produces a randomly selected one-character substring of x1 that is a variable if x1 is a variable.

If x1 is a list or record, ?x1 produces a randomly selected element, which is a variable, from x1.

If x1 is a set, ?x1 produces a randomly selected member of x1.

If x1 is a table, ?x1 produces the value of a randomly selected element of x1 as a variable.