I would like to add "required" validation to my created page custom attribute.

I put function "validateForm" in Attribute Controller.
But, it's thrown this function when save page meta datas.
(validateForm function was not called.)

I grep concrete5 sources to find call "validateForm" function.

profile, login, register, users...

so, it's called only from user custom attributes.

Do you know how to add validation to page custom attribute inputs?
Please tell me how.

thank you for reading!