Is there is a way to insert a validation of content inside a Long Text Entry?

I need to know if there is a way to insert a validation of content inside a Long Text Entry. For example, I want the users to always put a dot after the sentence they write. It doesn´t matter if the validation only checks for the presence of the dot, and not its position.

I'd suggest to look how it is implemented on GoogleForms, because it's very helpful and very convenient, and I'm sure you can find a way to implement it here and even improve it.

By the way, if it can be done with the use of CSS, I'd like to know how it can be done.

Thanks!

You cannot set validations and show form alerts with conditions (such as form required  message, or email address incorrect), but you could set up a condition to know when the long text entry has a dot in its value. 

Example: 

You could add text to your form and show it when the condition is met, here's a condition that will help you to show/hide fields based on other fields answer's: https://www.jotform.com/help/316-How-to-Show-or-Hide-Fields-Base-on-User-s-Answer 

Here's also a sample form: https://form.jotformpro.com/70878289390977 

Feel free  to clone it.