Regular expressions are patterns used to match sequences of characters in strings. PeerClick uses when setting up rules for referrals, Get, Url, V1-Vn and user agents.
By setting up a rule when choosing a regular expression matching method, you can write a criterion using a regular expression. For example, the Hel * o criterion will pass the values Hello, Helo, Heo, Helllllllllllo, etc., while the [0-9] criterion will only pass integer values from 0 to 9. A user with parameters taken into account by the regex will click on the tracker link fall under the criterion of the rule and, accordingly, be redirected along the path of this rule.