How to fix PHP Fatal error: Class ‘DOMDocument’ not found in /var/www/html/index.php on line 171 or similar error

NOTE: Received this error on a Centos 5 environment while trying to run a PHP script that makes use of the DOMDocument class

In the CLI (Command Line Interface) run the following command

{codecitation class=”brush: shell;”}
yum install php-xml
{/codecitation}

This will install XML support and will solve the DOMDocument issue