It appears that the following regex work differently.
Why \d and [\d] are different?
[A-PR-UWYZ]\d{1,2} and [A-PR-UWYZ][\d]{1,2}
This is getting into regex stuff, where maybe stackoverflow is a better resource? But when you put characters into brackets, you are telling regex to search for each character represented in the bracket. So [\d] is looking for any single character that is either a \ or a d character. Outside of brackets, regex evaluates \d as any digit. For US English charset [0-9] is equivalent to \d I believe.
