PHP - How to return the Server Validation Message back to Client side?

Question

The structure of the implementation of server side validation can be adopted by the following two methods.

Method one: The PHP script does the validation is the same one that provides the user with an input form. Say form_client_server.php

Method one: The PHP script does the validation is different from the one that provides the user with an input form. Say form_client.php (ie print the form for the user) and form_server.php (ie, the Action that will be triggered when the user submit the form by clicking submit button).

Here is the question:

In both cases, how the sever script can return messages (For example, error messages) to the page that displays the form?

If possible, I would like to see a tutorial/example/book chapter that gives some detailed information for this topics.

Thank you

Answer 1

您将消息插入到输出HTML。