How can the use of iframes impact page loading speed and what are some alternatives in PHP development?

Using iframes can impact page loading speed because each iframe requires an additional HTTP request to fetch its content, which can slow down the overall loading time of the page. One alternative in PHP development is to use server-side includes (SSI) or PHP includes to include external content directly into the main page, reducing the number of HTTP requests and improving loading speed.

<?php
include 'external-content.php';
?>