Regexp: ((a|b|\p{Nd}){1,2}|aaa|bbbb){1,2}

bab: Ok

aaca: Fail

aaabbbb: Ok

a0b: Ok

aa0aaa: Fail

b0aaa: Ok

Regexp: (\d{1,3}\.){3}\d{1,3}

1.2.3.4: Ok

1.22.333.44: Ok

1.2.3: Fail

1..2.3: Fail