RewriteEngine on

# Example request:
# http://domain.com/sites/demo/files/images/test.png

# Configuration options:

# 1) Files folder containing ONLY .htaccess
#    Result: Files from root site will be available and used.
#    Any file, e.g. images/test.png, will - from a browser's perspective - be loaded from
#    http://domain.com/sites/demo/files/images/test.png, which is why the .htaccess file
#    is required to redirect the request to:
#    http://domain.com/sites/demo/files/../../../files/images/test.png
#
# 2) Files folder contaning NO .htaccess file
#    Result: Only files found under sub site will be used

# The RegEx captures the file path relative to the folder containing the .htaccess file - e.g. images/test.png
RewriteRule ^(.*)$ ../../../files/$1