How does php add some fields to html forms?

For some special requirements, you can only use php (in the php file) to put some data into the hidden fields of the html form. How to do it? Thanks for some special requirements, you can only use php (in the php file) to put some data into the hidden fields of the html form.

How to do it?
Thank you.

Reply content:

For some special requirements, you can only use php (in the php file) to put some data into the hidden fields of the html form.

How to do it?
Thank you.

Modify it only in php. That is to say, you cannot modify the html template. The problem is where your value is placed in html.
So html or js needs to be modified.
Or you can use ajax asynchronous loading.
Only modify php. You can only include html code in the php file.

You can use a hidden.

Concatenate the html fields to be hidden, and add type = "hidden"

PHP files are subject to html code.

Php code-only

 ';?>

Concatenate the html fields to be hidden, and add type = "hidden"