What are alternative file formats that can be used instead of .txt for including content in PHP files?

Using alternative file formats such as .php or .html can be a better option for including content in PHP files as they allow for more flexibility in terms of embedding PHP code or HTML markup within the file. This can make it easier to manage and organize the content within the file and can also improve readability for developers working on the project.

<?php
include 'content.php'; // includes content from a separate PHP file
include 'content.html'; // includes content from a separate HTML file