Description:
------------
When running a script that is external (including it into another PHP file) opening that file will result in that external PHP being rendered as HTML text on the screen.

Test script:
---------------
(This is not a test script. It is an attempt to make a MediaWiki extension.)

$wgExtensionCredits['validextensionclass'][] = array(
       'path' => __FILE__,
       'name' => 'Vote Pages', 
       'url' => 'https://www.mediawiki.org/wiki/Extension:VotePage', 
       'description' => 'Allows unregistered and registered users to vote pages',
       'version'  => 1.0,
);

$rate = '<iframe frameborder="0" src="rate.html" height="91">'

return $rate;

Expected result:
----------------
The external PHP script should have ran.

Actual result:
--------------
It displays the code and any HTML that has been used in the external PHP file will be displayed instead.