You may want to provide a corresponding hint in the check-box's text (or at least its hover-text), because that's not exactly intuitive. Without the reg-exp checkbox being ticket one needs to provide a substring only that has to be contained somewhere in the response. With the check box ticked, it needs to match the entire response.
Here you can review submitted feature requests and vote up the ones you like! If you can't find the feature you want - go ahead and suggest your own idea. Ideas with the highest rating can be implemented in the product.