How to exclude specific file types from the following .htaccess rewrite rule?

Question

How can you exclude specific files types (xml and txt) from the following rewrite rule?

RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_URI} !(.*)/$
RewriteRule ^(.*)$ http://website.com/$1/ [QSA,L,R=301]

Answer 1

What about :

RewriteCond %{REQUEST_URI} !\.(xml|txt)$