[mod_rewrite] I don't want to open anything other than the specified file even if I access it with ".php".

Thank you for your help.

The site you are currently managing is
For example http://example.com/files/content
In response to the request, you can use .htaccess.

RewriteRule^files/([0-9A-Za-z_)]+)$1.php[QSA,L]

in the form
I try to display content.php.

However, with the current configuration,
http://example.com/content.php
The same file appears when accessed in .
If you look at the apache access log, sometimes you see a log of requests ending directly in .php, so if possible, I would like to try not to open anything other than the specified php file.

For example, as a file that permits a.php and b.php,
http://example.com/a.php
http://example.com/b.php
I can open it even if I request it in
I would like to display error.html for other requests containing ".php" such as http://example.com/content.php.

RewriteRule^files/([0-9A-Za-z_)]+)$1.php[QSA,L]
RewriteCond%{REQUEST_URI}!a.php$
RewriteCond%{REQUEST_URI}!b.php$ 
RewriteRule^([0-9A-Za-z_)]+).php$error.html[L]

Now that I've done this,
You can open it with a.php, b.php, but
Important
http://example.com/files/content
However, error.html is now displayed.

Please advise me on how to write it.
Thank you for your cooperation.