of_length n is a sample that always produces a string of fixed size n.

range min max s is a sample that always produces a string of size n, where min <= n < max, using the given sample s.

alpha_numeric is a sample that produces strings containing alhpa-numeric characthers.

numeric is a sample that produces strings containing numbers

alpha a sample that produces strings containing characters a-z, both upper and lower case.

upper is sample that always produces upper-case characters.

upper is sample that always produces lower-case characters.