Why is it considered a security risk to allow online editing of PHP files, and what measures can be taken to mitigate this risk?

Allowing online editing of PHP files can be a security risk because it gives unauthorized users the ability to inject malicious code or make unauthorized changes to the website. To mitigate this risk, one measure that can be taken is to disable the ability to edit PHP files from within the application itself and instead restrict file editing to authorized users with proper access controls.

// Disable editing of PHP files from within the application
define('DISALLOW_FILE_EDIT', true);