How to create validation for symbols?

Question

Yii

Good afternoon
How to create a validation rule according to the rule: Name_Firstname?

Answer 1

public function rules()
    {
        return [
            [
                'user_name', 
                'match', 
                'pattern'=>'/^[A-Z][A-Za-z]*_[A-Z][A-Za-z]*$/', 
            ],
        ];
    }

Answer 2

What is this "Name_Firstname" rule?
In any case, most likely we are talking about a regular expression, then here:
www.yiiframework.com/doc-2.0/guide-tutorial-core-v...