NSRegularExpression is used to inspect and manipulate strings using regular expressions. The interface is thread safe: The same NSRegularExpression object may be used to concurrently perform matching on multiple threads. To guard against regular expressions with extremely poor performance, the underlying matcher will abort after a certain number of steps. This is controlled using the GSRegularExpressionWorkLimit user default. The value of this default key represents the number of steps executed by the match engine, so it is only indirectly correlated with the time taken to execute the pattern, but it usually in the order of milliseconds. The preset 1500, setting value to 0 disables the work limit.