It is the "ASCII wrapper" feature IonCube has!
If you use the normal encoding option with Zend, IonCube, SourceGuardian or phpShield you'll need to ensure your customers upload your encoded script with the binary option selected in their FTP client. Most customers won't do this or even know how and they'll end up with corrupt files on their server. In other words: your scripts won't run.
IonCube has addressed this, allowing you to add an ASCII wrapper to your encoded files.
The default upload for a PHP file is ASCII, as ftp clients expect it just to be text. So using the ASCII wrapper avoids people complaining to you that your script isn't working due to corrupt files.