How to validate user input for textarea

I have a requirement to validate the user input on light box section. The field type is “textarea”.

Valid values=> comma separated number e.g. 1,2,3

Is it possible to do live validation? Please let me know how I can achieve this.

you can add handler to onEventSave event, which happens when user clicks ‘Save’ in the details form and check value there: … event.html