Should I separate PHP and HTML?

PHP and HTML should be kept separate for the cleanliness of code. Templates or frameworks provide a way to do this by separating PHP for handling the logic and data and HTML for handling the structure and presentation. Keeping them separate will make your code easier to maintain, debug, and scale. Still, PHP and HTML come together, in all actuality, in projects that are on the more accessible side of things, or in older codebases where dynamic content was created directly inside the HTML files. One surefire way to keep things this way is through a templating engine or MVC framework.