Use the form button and check for each pattern if some kind of value is valid or not. This is just a regex example, there is much more you can do with regular expressions.
All patterns are optimized to use with the PHP function preg_match (note the leading and the trailing slash).
This decimal check allows a decimal number with max 5 digits before the "." and 1 or 2 decimals.
This postal code is a combination of four numbers and 2 letters (f.e. 1000 AB). With this pattern its allowed to use caps and small caps and a single space or not between numbers and letters.
This example checks real world e-mail addresses, but the pattern is limited to the lack of knowledge about the domain names and users. But the pattern takes care about unallowed characters and combinations.