I have a question regarding configuring apache for the following setting:
You can use this code in your DOCUMENT_ROOT/.htaccess
file:
RewriteEngine On
RewriteBase /
# if not a file
RewriteCond %{REQUEST_FILENAME} !-f
# if not a directory
RewriteCond %{REQUEST_FILENAME} !-d
# if URI is not starting with /_dev/ then rewrite to /_dev/<uri>
RewriteRule ^((?!_dev/).*)$ /_dev/$1 [L,NC]