by Peshmerge Morad on WordPress.org
A WordPress plugin and GravityForms addon to enable users to use regex string on text input field to control user input.

General tab of the Regex Textfield field in the form editor.
This plugin is created to enable WordPress site owners to specify a regex string to be used with Gravity Forms text fields.
Once a regex string is specified, the user can’t submit that form until the user enters a text that comply with the regex string.