Do I need a !DOCTYPE declaration in a php file with html?

Question

I have a php file with my website content in it. The file needs to be .php because i get some variables first and then use it later in the website content. Like this example

Answer 1

Yes, you should have the DOCTYPE declaration, since what you send the browser is HTML, not PHP.

The declaration tells the browser that you are using HTML 5 and tells it how to render it.