A system receives a request to create a template. Responsive to the request, the system displays a user interface including at least a preview and configuration region, and a template variables region. While displaying the user interface, the system receives user input that selects a respective variable for inclusion in the template. Responsive to the user input, the system updates the configurable preview of the template to include the respective variable, and displays user interface elements used to define input-acceptance rules for the respective variable. The system receives user input at the user interface elements to define an input-acceptance rule having at least one condition that must be satisfied before input will be accepted via the respective variable when that respective variable is used in conjunction with the template. Responsive to the user input at the user interface elements, the system associates the respective variable with the input-acceptance rule.