What are some key principles to follow when mixing PHP and HTML code in a project?

When mixing PHP and HTML code in a project, it is important to maintain separation of concerns by keeping logic separate from presentation. This can be achieved by using PHP to generate dynamic content and HTML to structure the layout. Additionally, using PHP tags appropriately within the HTML code can help keep the codebase organized and maintain readability.

<?php
// Example of mixing PHP and HTML code in a project
$dynamic_content = "Hello, World!";
?>

<!DOCTYPE html>
<html>
<head>
    <title>PHP HTML Mixing Example</title>
</head>
<body>
    <h1><?php echo $dynamic_content; ?></h1>
    <p>This is an example of mixing PHP and HTML code in a project.</p>
</body>
</html>