How to create custom form_validation rule in Codeigniter?

Question

CodeIgniter

Hello. Please tell me how to create my own form_validation rule in Codeigniter 3. It is necessary to make a rule for checking the Cyrillic alphabet. I tried to use the "alpha" rule, but it does not accept Cyrillic. I ask for your help. Perhaps someone already has a created rule, or pieces of code, share, I will be very grateful.
I searched on the Internet, found only here , the links are not working, the author abandoned the blog a long time ago, tried to contact him, in response to silence. Author's profile on Habré.
Perhaps someone has his actual contact details, please also share them. Thank you.

Answer 1

The manual says: https://www.codeigniter.com/userguide3/libraries/f...

Answer 2

In the application/libraries directory, create the MY_Form_validation class, which inherits from CI_Form_validation. This is where you describe your data validation methods.