RewriteEngine On
RewriteRule ^(?!foldername/)(.*)$ foldername/$1 [L,NC]
DirectoryIndex index.php
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . index.php [L]
RewriteEngine On
RewriteRule ^(?!foldername/)(.*)$ foldername/$1 [L,NC]
DirectoryIndex index.php
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . index.php [L]