How to display the value of a PHP constant correctly?

Question

PHP

This is a basic PHP task, but there are doubts about the correctness of the output.
Here is the task: prntscr.com/ip2uou
Namely, point - 2. It is
not clear that you need to create a separate page with the .html extension, or create a .php file and place a constant there and below the html code of the page, but then it is not clear why it is written - (mandatory with DOCTYPE and all basic HTML tags: html, head, body)
Why write a DOCTYPE if the document is php? Or I do not understand something?
In general, I did this, created a php file and put the following there: prntscr.com/ip2yqo
Is that correct?

Answer 1

So will it be right?

Correctly.

Why write a DOCTYPE if the document is php?

Browsers do not know how to execute php, ready-made html pages always come to them. But on the server, this page is usually generated using some kind of executable file (in this case, it is a php file).