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

The same rules for HTML apply equally, whether they're plain HTML files, or HTML files with embedded PHP. YOu need a doctype in every circumstance you'd need one in plain HTML.

By the way, there's whitespace between the end of the first block oh PHP code and the doctype. I seem to remember that whitespace before the doctype can be problematic (though that might only apply to XHTML)