How can including HTML files in PHP or using the here document syntax be a more effective alternative to converting HTML to PHP?

When converting HTML files to PHP, it can be time-consuming and cumbersome to manually add PHP tags and concatenate variables throughout the HTML code. A more effective alternative is to include HTML files directly in PHP using the `include` or `require` functions, or by using the here document syntax to embed HTML within PHP code without the need for concatenation.

<?php
// Using include function to include an external HTML file
include 'header.html';

// Using here document syntax to embed HTML within PHP code
echo <<<HTML
<div>
    <h1>Welcome to our website</h1>
    <p>This is a paragraph of text.</p>
</div>
HTML;

// Using require function to include a footer HTML file
require 'footer.html';
?>