frame.php

См. документацию.

<?
//This file still exists because of SiteUpdate features.
//When you reinstall updates (main 17.1.0 with previous ones),
//SiteUpdate includes old version of 'include.php' which invokes Frame::shouldBeEnabled().
 
$oldClassName = "Bitrix\\Main\\Page\\Frame";
$newClassName = "Bitrix\\Main\\Composite\\Engine";
$newClassFile = $_SERVER["DOCUMENT_ROOT"]."/bitrix/modules/main/lib/composite/engine.php";
 
if (!class_exists($oldClassName, false))
{
    if (class_exists($newClassName, false))
    {
        class_alias($newClassName, $oldClassName, false);
    }
    else if (file_exists($newClassFile))
    {
        require_once($newClassFile);
    }
}