For text questions, the only available validation rule restricts the field to alphabetic characters.

1. Go to the Rules sidepanel as described in Access the Rules section.
2. On the Rules sidepanel, select Add Rule and then select Doesn't Contain
   A Validation Rule dialog appears.

   
3. In the Error Message field, enter an error message that should appear for site users when the answer is invalid.
   The error message appears for site users when the answer is missing or invalid.