diff --git a/introduction.htm b/introduction.htm index dfbbb88a..6d9128d8 100644 --- a/introduction.htm +++ b/introduction.htm @@ -87,7 +87,7 @@ tended to be hard-coded to the C-locale, consequently this was not an issue for them). That leaves us with the following regular expression to validate credit card number formats:

-

(\d{4}[- ]){3}\d

+

(\d{4}[- ]){3}\d{4}

Here the parenthesis act to group (and mark for future reference) sub-expressions, and the {4} means "repeat