Why does PHP Storm highlight variables in red if they are included from another file?

Question

phpstorm

There are 2 files in the project: index.php and config.php.

config.php included in index.php
file config.php index.php
$workmode = 1;

require('config.php');
if ($workmode == 0) {
    echo 'Проверка отключена.';
    exit;
}

Here $workmode is underlined in red.

However, despite this, in the index.php file, the variables defined in the config are highlighted in red.
Writes Undefined variable '$workmode' . The script itself works.

How to fix it?