For creating the field validator - you need to use validators as described in the Academy article here. As for the ESQ in the Freedom UI page - unfrotunately we currently don't have any documentation on it, but we've created a task for our core R&D team to write the specification for ESQ usage in the Freedom UI page.
After verifying all the necessary information regarding specification for ESQ usage, I want to inform you that this task has been created and accepted. The process of writing such documentation may take some time, so for the moment you need to wait a while.
Thank you for your patience and understanding in this matter.