Your interface requests a specific kind of text input from the user, formatted in a certain
way. That format is familiar and well defined, and you don’t expect any users to need to
deviate from the format you expect. Examples include credit card information, local telephone
numbers, and license strings or numbers.
It’s generally a bad idea to use this pattern for any data in which the preferred format may
vary from user to user. Consider especially what might happen if your interface is used in
other countries. Names, addresses, postal codes, and telephone numbers all have different
standard formats in different places. Consider using Forgiving Format in those cases.