Every question can be required by checking the Response Required box in its question page. Some question types, such as text, allow validating that the input is in a certain range, such as 1 to 10000. Both browser and server side validation checks are performed.
For additional validation, use a Question Style such as E-mail, Number, and Date. These styles check for the appropriate content and prevent the respondent from continuing until a valid entry is entered. These styles only check input in the browser and do not validate input on the server.
You can create your own Question Styles to check the content of fields in your own ways. Check the Styles Library in the Support section of www.cogix.com.
Data validation messages can be customized as described in Custom Validation Messages.
Next: Custom Validation Messages