I am cleaning some old code and discovered a guide inside a .htaccess that does not seem sensible in my experience.

RewriteEngine On
RewriteCond %{REQUEST_URI} !^(/listener/v2/bbin/)
RewriteRule ^(.*)$ /listener/v3/v210_ui.php$1 [L]

This .htaccess file is situated in <docroot>/listener/v2/. Unless of course I am mistaken, the rule essentially is proclaiming that when the request is perfect for personal files within this directory, internally redirect it to /listener/v3/v210_ui.php.

My confusion comes from the truth that you will find lots of files within this directory. Shall We Be Held missing something? Did that old developer simply not cleanup after themselves?

You are close...

When the request is perfect for an origin in /listener/v2/bbin/ and it has doesn't begin with /listener/v2/bbin/ within the URI redirect it to /listener/v3/v210_ui.php and append the URI.

Now why you are carrying this out I can not answer. Educate yourself on [cde].