Web developers are well used to doing certain data validations to ensure people are entering correct information into their websites. A perfect example of this is the common email address, which must follow a format of being in the format (something)@some.domain.(com) where the (com) part, the so-called Top-Level Domain (TLD) has to be one of a finite series of words - either "com", "org", "net", a limited number of others, plus the defined two-letter country codes.