In SMF2.0, regular expressions can be used in the Advanced Settings when creating or editing a custom profile field.

NOTE - When entering regular expressions (regex), you must surround them with delimiters such as tildes (~) or double quotes ("), otherwise they will not work and there will be no warning of this failure. Two examples of the correct way of entering regular expressions for SMF are: ~[12][0-9]{3}~ or "[12][0-9]{3}"

The input mask is important for your forum's security. Validating the input from a user can help to ensure that data is not used in a way you do not expect. Here are some examples of simple regular expressions:

• "[A-Za-z]+" - Match all upper and lower case alphabet characters.
• "[0-9]+" - Match all numeric characters.
• "[A-Za-z0-9]{7}" - Match all upper and lower case alphabet and numeric characters seven times.
• "[^0-9]?" - Forbid any number from being matched.
• "^([A-Fa-f0-9]{3}|[A-Fa-f0-9]{6})$" - Only allow 3 or 6 character hexcodes.

Additionally, special metacharacters such as ?+*^$ and {xx} can be defined:

• ? - None or one match of the preceding expression.
• + - One or more matches of the preceding expression.
• * - None or more matches of the preceding expression.
• {n} - Matches the preceding expression exactly n times.
• {n,} - Matches the preceding expression at least n times.
• {,n} - Matches the preceding expression no more than n times.
• {n,m} - Matches the preceding expression at least n times, but no more than m times.
• ^ - The start of the string.
• $ - The end of the string.
• \ - Escapes the next character.