How can I redirect from a php page to html page when the user click validate

Question

I have a form where the user enter his personal information
Then I managed those values entered by the user via php
And I have as well to control the way he wrote every thing in the form such as:
Email should contain:@ and so on …..

But when he doesn’t respect those things I have to redirect him to the form(html) and print him a message inside the html page=form saying:
This email is not valid

HOW CAN I DO IT PLEASE

Answer 1

you don't have to redirect him, you can just add a pattern with a regex to your HTML input like so:
<input type="email" name="email" pattern="[a-z0-9._%+-]+@[a-z0-9.-]+\.[a-z]{2,4}$ title="the current email is not valid">