Canadian Passport Pattern

(?i:\bAT[0-9]{2} [0-9]{4} [0-9]{4} [0-9]{4} [0-9]{4}\b)

Matches an alphanumeric string of the format ATNN NNNN NNNN NNNN NNNN delimited by space. Begins with "AT" (not case-sensitive) followed by an 18-digit number.

1

(?i:\bAT[0-9]{18}\b)

Matches an alphanumeric string of the format ATNNNNNNNNNNNNNNNNNN without a delimiter. Begins with "AT" (not case-sensitive) followed by an 18-digit number.

1