How important is the separation of HTML and PHP code for maintaining clean and reusable code in PHP?

Separating HTML and PHP code is crucial for maintaining clean and reusable code in PHP. By keeping these two languages separate, it makes the code easier to read, understand, and maintain. It also allows for better organization and separation of concerns, making it easier to make changes or updates in the future.

<?php
// PHP code
$variable = "Hello, World!";
?>

<!DOCTYPE html>
<html>
<head>
    <title>Example</title>
</head>
<body>
    <h1><?php echo $variable; ?></h1>
</body>
</html>