# Lists: [ and ]

Quite often we want to be able to specify a small set of allowed characters. The list operator [ ] allows us to do this. by putting characters in between '[' and ']' we are saying that only these characters are allowed here.

We can chain together lists to build more complex sequences

## Simple list

A simple list specifies one or more allowed characters.

List | Description | Matches | Doesn't match
[aeiou] | Any lower case vowel | a, e, i, o, u | A, b, c, I
[AEIOU] | Any upper case vowel | A, E, I, O, U | a, b, B, i
[AEIUOaeiou] | Any upper or lower case vowel | A, E, I, O, U, a, e, i, o, u | B, b, J, j
[0123] | Any single number from 1, 2, or 3 | 1, 2, or 3 | 4, 5, 6