Hi Thorn,
Unfortunately there is no form validation other than marking a field as Required.
If you’d like to try your hand at this customization, I’d recommend starting off by taking a look at our Themer’s Guide, which can show you which templates can be edited and copied in order to achieve the results that you are looking for.
If this functionality is a requirement for your intended project, I’d suggest that a third-party developer would be the best way to make this feature happen on a short timeline. ? We maintain a list of developers who work with our plugins on our Knowledgebase here:
https://theeventscalendar.com/knowledgebase/find-a-customizer/
You can also add this idea to our Feature Requests, as we tend to implement ideas based on customer feedback, so your input is greatly appreciated:
https://tribe.uservoice.com/forums/195723-feature-ideas
Let me know if you have any other questions on this topic!
Thanks,
Jaime